It was during this time that Lilly made her sword from a blade of the Vertibird that crashed near Klamath. It was also during this time that she developed multiple personality disorder, this personality "Leo" would "show" her how to craft the blade. With the fall of Unity, the destruction of the Cathedral and the death of the Master, whom she didn't like, she decided it was time to go home.
While living at Jacobstown, she began receiving help from Doctor Henry for her schizophrenia, brought on by excessive Stealth Boy usage and manifesting itself as a split-personality named "Leo," with anti-psychotics drugs. The side effects of the drugs however is memory loss. Unwilling to forget her past, in particular her grandchildren Jimmy and Becky, she chooses to take her medicine at half-doses. An act personified by listening to a holotape of the last time she visited her grandchildren.
The "Leo" personality manifests itself as a malicious deviant and sociopathic voice she can communicate with, "he" will give instructions in battle and tell her to do "terrible things."  "He" in turn doesn't like being called a voice in her head. In stark contrast is Lily's natural personality, friendly, helpful, and pleasant. Due to her nightkin training, she can help the Courier with their stealth. While she claims to not like guns that doesn't mean she is incapable of doing so, just that she and "Leo" prefer to use bladed melee weapons.
When Doctor Henry began his work on developing a cure for the nightkin schizophrenia she asked his permission to help. She even still wishing to help after he informed her of the risk of permanent brain damage. Should the Courier help her and Doctor Henry with the completion of the cure, Jacobstown will prosper. Furthermore should the Courier help convince her that she was correct to take her medicine at half doses she will eventually leave Jacobstown to seek the remnants of her past. However, if she is convinced that she should take the entire dose every time she will forget the importance of her past and throw away her holotape. Or, if she is convinced to stop taking her medicine then she will be consumed by the Leo personality becoming nothing more than a ravening beast.
Lily and Leo: At a certain point, if Lily Bowen is the active companion, the player character may begin to hear a recording of children greeting their grandmother. This signals the start of Lily's unmarked quest.
Encouraged by the Courier to take her medication regularly, Lily's mind eventually attained a semblance of clarity. Her memories dulled by the pills, she cast aside the recording of her grandchildren, no longer remembering its significance.
Encourage Lily to take her medication regularly in her unmarked quest, Lily and Leo.
Lily continued to take her medicine at half-doses, and although she remembered her grandchildren, her mind remained muddled and confused. Eventually, she parted ways with the Courier and traveled west, seeking the remnants of her past.
Encourage Lily to continue taking her medicine at half-doses in her unmarked quest, Lily and Leo; or do not complete the quest.
Encouraged by the Courier to stop taking her medication altogether, Lily's instabilities grew worse with each passing day. Eventually she became little more than a ravening beast, the kindly old grandmother subsumed beneath the rage.
Additionally, Lily has a third companion weapon, a power fist variant called Lily's gauntlet. This weapon is not initially in Lily's inventory but may be given to her as part of a script that ensures all companions retain their special weapons.
Lily is limited in the weapons she can use, and can only equip weapons from the following list. Lily's default assault carbine's high DPS effects which weapons she will equip. There are only two holdout weapons which Lily is capable of using: frag grenades and plasma grenades.
Her husband used to make a particularly strong moonshine, of which she partook from time to time.
If one enters with Lily inside the cafeteria of Vault 3, she will comment about herself when she was a small girl and she will remember her first kiss. This will also occur upon entering Vault 11, Vault 19 and Vault 22.
As a nightkin, Lily is also significantly faster than the player character. It is not uncommon for her to charge ahead to engage a target, which can be problematic when dealing with creatures like deathclaws.
When Lily is a companion, if she is reduced to one half of her hit points, she will suffer a "psychotic break" and will be in aggressive mode until it fades. The player character is unable to give Lily commands or interact with her until this break subsides. She will also repeat a mantra, quickly counting to ten repetitively to calm herself down.
While Lily is not a companion, cazadores may attack Jacobstown and kill her.
If the player character asks her to be aggressive she will comment saying, "That's exactly what Leo told me to do!"
While approaching tribal village with Lily, she will ask, "Oh dear, did I do all of this?"
When enemies are identified, Lily will frequently state "Get behind Grandma" and then place herself between the player character and the enemies.
When crouched, Lily enters her own sneak mode, where she activates a permanent Stealth Boy until the player character stops sneaking. When in this mode, it is hard to see Lily in front, or between the player character and an opponent, and one can frequently shoot her accidentally, because of her tendency to stand between the Courier and their enemies. This can sometimes be countered by telling her to "back up."
The super mutants at Jacobstown may comment on Lily, in which they whisper to the player character, "Better watch out. Lily's been babbling about her grandkids again."
Lily is noticeably shorter than other nightkin, such as Keene.
The following is based on developer test content cut from Fallout: New Vegas and has not been confirmed by canon sources.
PCPlaystation 3Xbox 360 Lily's vertibird sword and assault carbine may occasionally clip into one another, causing whichever one she's using to have the other hanging from it. The sword may also be replaced entirely by the gun. She will not shoot with the gun, however; she will continue to use it as a melee weapon. Opening her companion wheel and forcing her to switch between melee and ranged attacks a couple times will fix this glitch. [verified]
PCPlaystation 3Xbox 360 Sometimes when going into stealth mode, Lily will say her normal line, "Oh, don't you worry about me dearie, your grandma knows how to stay quiet," but will repeat it every 20–30 seconds. [verified]
Xbox 360 Even before recruiting, if you talk to Lily, she will comment on things like Lucky 38 or Benny being killed. [verified]
Xbox 360 After killing the mercenaries that are at Jacobstown she may randomly attack the player then fall unconscious. [verified]
PCPlaystation 3Xbox 360 On rare occasions, Lily may die before she is recruited as a companion in a non-hardcore game. [verified]
PC Sometimes, when Lily is equipped with Oh, Baby! she will randomly lose the weapon. It will no longer be in her hands or in her inventory, where it would normally go if it were to break from use. [verified]
PC If Lily is asked to use ranged weapons, she may not take out her assault carbine, and instead stay with her vertibird sword, or bumper sword if it is in her inventory. Even if switched back to melee, she will still stand near the courier, trying to use a melee weapon as a ranged weapon. This can be fixed by switching her back to ranged, then back to melee again; however, there is not a fix to make her use her Assault Carbine, because the next time you switch her to ranged, the bug occurs again. [verified]
Xbox 360 If the player dismisses Lily to the Lucky 38 penthouse, she will not always make it there, but instead found in the Casino section, able to recruit again and dismiss to the penthouse without issues. [verified]
PCXbox 360 When the player character is sneaking, Lily may not enter sneak mode along with the player, and instead will walk along as if the player was not sneaking. [verified]
PCXbox 360 If the player dismisses Lily while they are sneaking, Lily will remain in stealth mode until recruited again.[verified]
PCXbox 360 Lily may disappear on the way to Jacobstown during Guess Who I Saw Today, if she is sent to the Lucky 38 and then asked to take Doctor Henry's test for the Stealth Boy Mark II without re-hiring her. However, it will still be possible to complete the mission regardless of whether or not she's actually there, though she may not be hirable again unless somehow found. [verified]
To fix this, either access the dismissal terminal and dismiss all companions, or reload a previous save. The former should bring Lily back to the Lucky 38's presidential suite.
↑ 2.02.1Lily Bowen: "Eithergrandma needs to cut back on grandpa's special moonshine, or she's been poisoned." (Lily.txt) Note: This line is spoken when Lily is poisoned by a creature.
↑ 3.03.1The Courier: "Jimmy? Little Jimmy - my, how you're grown up. So good of you to come visit your grandma." The Courier: "Who's Jimmy?" Lily Bowen: "Oh, Jimmy, don't you go being silly now! Come over here and give your grandma some sugar!" (Lily.txt)
↑ 5.05.15.2The Courier: "I'm sure. I'd rather you didn't have any psychotic breaks, even if it means you aren't as strong." Lily Bowen: "Well, all right, then, dearie. I suppose I'll have my holotapes to remind me of Becky and Jimmy...." (Lily.txt)
↑ 6.06.1The Courier: "Where did you come from?" Lily Bowen: "I grew up in Vault 17. I never even saw the sun until I was 75 years old - that was when Super mutants raided the Vault and carried a lot of us off. Yes, Leo, I'm getting to that part!They made me one of them, and they put me to work in an army that was going to conquer California." (Lily.txt) Note:Lily Bowen's birth date (2078) and stated age (75) when leaving the Vault. Amended to fit the established timeline.
↑Lily Bowen: "My, my, this reminds me of when I was a girl. Right over there would have been where your grandpa and I had our first kiss!" (Lily.txt) Note: This line is spoken when entering the cafeteria of a vault.
↑The Courier: "You were a soldier?" Lily Bowen: "A spy. Sometimes an assassin. I killed a lot of folks for the Master. Yes, Leo, you helped, too." (Lily.txt)
↑The Courier: "Earlier, it seemed like you knew Tabitha. What's the story there?" Lily Bowen: "Tabitha was grandma's squad leader when we both worked for the Master. She wasn't very nice at all, but she was good at the chopping. Almost as good as Leo...." (Lily.txt)
↑Lily Bowen: "Tabitha! You naughty, naughty girl! Leo remembers what you did!" (Lily.txt)
↑The Courier: "Where'd you get that sword?" Lily Bowen: "This old thing? Oh, I scavenged it off a wreck in Klamath. Leo showed me how to make it all ready for chopping, didn't you, Leo?" (Lily.txt)
↑The Courier: "Who was the Master?" Lily Bowen: "Oh, he was a nasty man, dearie. You don't want to know about him. He was the one who made that Super mutant army I told you about." (Lily.txt)
↑The Courier: "What happened then?" Lily Bowen: "That wicked old Master got what was coming to him, that's what! After his cathedral blew up, I decided it was high time to go home." (Lily.txt)
↑Fallout: New Vegas Official Game Guide p. 44: "Part 3: Other Factions: Mojave Wasteland; Super Mutants Unfortunately for Marcus, not all of the Nightkin were content to live under his rules. Davison (who currently talks to a Brahmin Skull named Antler in the bowels of the REPCONN Test Site) and Tabitha (who broadcasts her particular brand of insanity from Black Mountain) broke off on their own, eventually winding up with their own dysfunctional Super Mutant communities. Though Marcus is disappointed at how things turned out, he does the best he can to take care of Lily and the other Super Mutants and Nightkin at Jacobstown."
↑The Courier: "What do you do in Jacobstown?" Lily Bowen: "I watch over the Bighorners. They're sweet, gentle creatures, but sometimes they get ornery. Just like my grandkids!" (Lily.txt)
↑The Courier: "I'm looking into the Nightstalker mutation. Want to come along with me?" Lily Bowen: "Oooh, those Nightstalkers, always killing my Bighorners! It'll be nice to give them a piece of my mind!" (Lily.txt)
↑The Courier: "I'd like to help. What do you need me to do?" Henry: "I'm not convinced that the Nightstalker mutation is a natural one, and I need someone to investigate their lair for proof. Some of the Super Mutants have looked around as well, but they've come back empty-handed. Perhaps a pair of fresh eyes will have better luck. Lily might be interested in coming with you - she's lost a few of her Bighorners to Nightstalker attacks and would enjoy a little revenge." (VRemDoctorHenry.txt)
↑The Courier: "What kind of medicine are you taking?" Lily Bowen: "Doctor Henry calls them "anti-psychotics." I don't know what they're supposed to do, they just make my memory fuzzy." (Lily.txt)
↑The Courier: "Why is it hard to remember them?" Lily Bowen: "It's my medicine, dearie. It keeps me calm, but it makes my memory go all fuzzy. That's why I only take my dosage every other time. That way at least I remember their faces." (Lily.txt)
↑ 20.020.1The Courier: "What happened in that fight back there?" Lily Bowen: "Oh, pumpkin, grandma's sorry about that. Sometimes she gets mad and listens to Leo when she really shouldn't. The medicine is supposed to help with that, but sometimes grandma doesn't take it." (Lily.txt)
↑ 21.021.1The Courier: "Who is Leo?" Lily Bowen: "Leo is a very bad man, pumpkin! Yes you are, Leo, don't try to deny it!He tells me to do things, terrible things, and sometimes the medicine isn't enough to keep him quiet!" (Lily.txt)
↑The Courier: "You should keep taking your meds every other time. It's worth the risk to remember your family." Lily Bowen: "That's sweet of you, dearie. I'll try to be better about controlling myself if I see you try to sneak away." (Lily.txt)
↑The Courier: "What was that recording you were listening to?" Lily Bowen: "Oh, that old thing? That's a holotape from the last time I visited my grandkids. Such sweet little children, you know. Little angels. Sometimes it's hard to remember them, so I take that old tape out from time to time and listen." (Lily.txt)
↑The Courier: "So he's just a voice you hear in your head?" Lily Bowen: "You shouldn't say things like that where Leo can hear you, dearie. He doesn't like it." (Lily.txt)
↑ 25.025.1The Courier: "Why Lily and not some other Nightkin?" Henry: "Lily is eccentric, certainly, but I've never felt she was dangerous. More importantly, she asked if she could help me in some way. I've told her about the risks, and she still insists on helping me." (VRemDoctorHenry.txt)
↑The Courier: "Tell me about yourself." Lily Bowen: "Aww, someone wants to hear grandma's stories! What would you like to hear, pumpkin?" (Lily.txt)
↑The Courier: "What's the best way for me to use your skills?" Lily Bowen: "Isn't that sweet of you to fret about me? Such a good boy/girl. I can always help you stay hidden from the bad people so you won't get in trouble. I don't mind fighting - especially to protect you, dearie - but I don't like guns. Give me a good chopper, and Leo and I will go right to work!" (Lily.txt)
↑The Courier: "I want you to use ranged weapons." Lily Bowen: "Well, if you insist, but Leo isn't going to like it much." (Lily.txt)
↑The Courier: "Doctor Henry wants to know if you'll continue to wear the Mark II prototype." Lily Bowen: "Of course I will, dearie, if it's helpful. Don't you worry what will happen to little old me. I'm tougher than I look!" (Lily.txt)
↑The Courier: "There's a risk that the mental damage will be permanent." Lily Bowen: "Of course, dearie." The Courier: "You can always say no." Lily Bowen: "I know that, dearie." (Lily.txt)
↑The Courier: "Did you still want to help Doctor Henry run his experiment?" Lily Bowen: "Of course, dearie. I know it's dangerous, but it'll all turn out for the best, you'll see. I'll go to him now - it would be rude to keep him waiting!" (Lily.txt)
↑The Courier: "What are the risks of the experiment?" Henry: "Possibly immediate and permanent mental damage. There's a reason the Stealth Boy Mark IIs never got beyond the prototype stage. Lily already has a pre-existing condition, and the experiment will likely make things worse for her." (VRemDoctorHenry.txt)
↑The Courier: "What do you want to do?" Henry: "I'm close to the cure, I can feel it. Lily's continued help will give me the last bit of data that I need." (VRemDoctorHenry.txt)