Cominsky was part of the Fire Breathers' final mission to prevent the progress of a Scorched horde by sealing the Big Bend Tunnel using explosives. Her code phrase for the Fire Breathers master terminal was "Nuka Addict," a reference to a time when she found a case of Nuka-Cola and did not save any to be shared with the rest of the squad.
Her corpse can be found in the Big Bend Tunnel, near the end of a side tunnel with railroad tracks running south that is at a right angle to the tracks that run through the tunnel, presumably having been killed while setting the explosives.
Sgt. Cominsky appears only in Fallout 76.