Lucy’s mom, Rose MacLean, doesn’t die off‑screen of an illness like Lucy was told – she’s bombed, turned into a ghoul, exploited, and finally mercy‑killed by Lucy in the Fallout TV series.

What really happened to Lucy’s mom in Fallout?

  • Rose becomes suspicious of Vault-Tec’s “the surface is deadly” doctrine and takes Lucy and Norm out of Vault 33 to live in Shady Sands with Moldaver.
  • Hank (Lucy’s dad) tracks them down, takes the kids back to the vault, and lies that Rose died in the “Plague of ’77,” having her “burial” faked for the children.
  • Later, Hank arranges for a nuclear device to be detonated in Shady Sands; the blast and radiation destroy the settlement and irradiate Rose, turning her into a ghoul instead of killing her outright.
  • By 2296, Rose is a heavily deteriorated, non‑verbal ghoul kept by Lee Moldaver, essentially alive but in a state many characters view as worse than death.

The reveal and Lucy’s choice

  • In the season 1 finale, Lucy confronts Hank at Griffith Observatory and learns the truth: the nearly unrecognizable ghoul sitting by Moldaver is her mother, Rose.
  • After Moldaver dies and the Brotherhood attacks, Lucy is left with her ghoul mother, an unconscious Maximus, and the Ghoul offering her a chance to team up and go after Hank.
  • Realizing her mother has been suffering for years in this state and is barely conscious, Lucy decides to end that suffering; she takes the gun and shoots Rose in the head, a clear mercy kill.
  • Lucy then leaves with the Ghoul to hunt Hank, while Rose’s body remains where she died, with Moldaver later sitting beside her as she herself succumbs to her wounds.

In short

  • Rose was exiled topside when Hank destroyed Shady Sands.
  • The radiation ghoulified her rather than killing her.
  • Years later, Lucy finds her as a barely living ghoul.
  • Lucy shoots her mother to give her a quicker, kinder death and then walks into the wasteland to pursue Hank.

Bottom note: Information gathered from public forums or data available on the internet and portrayed here.