At the beginning of the season, Brooke seems the most likely candidate to be the final girl because of how innocent she is. But as she grows tougher, murdering Montana and serving years in prison, we were more skeptical she'd make it out alive even if Donna revived her at her lethal injection execution. Emma Roberts pretty much always dies, whether she's sawed in half in Freak Show or strangled to death in Coven.
But Brooke survives by the skin of her teeth. After escaping a creepy serial killer on the road, she and Donna make it to Camp Redwood for the showdown, determined to take down Margaret. But in a brawl, Margaret shoots her in the abdomen, and it's pretty much assumed Brooke will bleed out to death. Donna thinks she's dead, but Ray finds out she's alive and takes her out of the camp's vicinities. When she passes out at the entrance, we can assume Ray or someone else calls 911 from a phone booth to get her to a hospital.
Brooke goes MIA for a long time, and Donna assumes she's dead. When Bobby Jr. tells Donna he's been getting mysterious checks throughout his life, they finally (and somewhat conveniently) track down Brooke in Pineville, OR. They meet Brooke, who looks freakishly good for her age, attributing her luminous skin to fillers. She tells them that when she got out of the hospital, she just went north, where she met her dermatologist husband and had two kids with him. Brooke explains to Bobby that his father gave her hope, and that's why she wanted to give him a chance at a functional, nonmurdery life.