Clara's note to mom is a paper note in Fallout 76.
The note can be found in a doghouse in the back yard of the red house across the street from the Vault 76 overseer's old home in Sutton.
Mom, I'm so sorry that my research got you addicted to this... swill. I'll get revenge on the bastards in marketing that did this, I swear to you.
I love you and I miss you so much.