|“|| Gail: Do you know God gentleman? |
Dean: Oh yeah. Yeah, we're besties.
— Gail and Dean Winchester
Gail Peterson is the mother of psychic Magda Peterson.
Gail's daughter was born with powerful psychic abilities, which led her to cause a car accident while she and Gail were arguing.
Gail was left with damaged nerves and constant pain, and following the accident, Gail became fanatically religious. She cut the family off from the world, faked Magda's death and locked her in the basement of their home. Believing Magda to be possessed by Lucifer, Gail would force Magda to whip herself to try to get the Devil out of her.
Following the death of Olivia Sanchez, Gail and her family were approached by Sam and Dean Winchester. The brothers initially suspected her daughter was a vengeful spirit, but Sam found out otherwise after overhearing a conversation between Elijah and Abraham. The two men captured Sam and showed to him Gail's "cursed" abilities, though Sam argued that she was not possessed, but merely a psychic, who had the chance to control her powers and do good.
Gail was nevertheless unconvinced by Sam's words and Sam remained tied up. She told Sam that her daughter was evil and that she was a murderer. She revealed what Magda did while she was driving, and how it affected her. Gail said what Magda had committed a sin, and punishing her daily was a means to purify her.
Gail then served the family dinner, with the intention of sending everyone to Heaven so they could be together. Abraham was poisoned by the food before he realized his wife's plans. Gail ordered Elijah to follow suit, but Magda saved him by telekinetically flinging away his spoon.
Furious, Gail picked up a knife and tried to stab Magda, but Elijah got in the way and was killed. When Gail tried again, Magda used her powers to turn Gail's knife around. Declaring she was not the Devil, Magda planned to get revenge on her mother by killing her, but Sam's frantic pleas for her to reconsider spared Gail from death. Gail was instead taken away by the police, while her daughter was expected to go live with an aunt.