Sammy Weathers was captured by Caesar's Legion, along with her mother and brother, while relocating in the Mojave Wasteland. Her abusive father, Frank Weathers, abandoned them to the Legion.
Left My Heart: Frank Weather's family was captured and made slaves by the Legion. Instead of him manning up, he tasks the player with freeing his family.
PC When arriving in Cottonwood Cove, Sammy may already be dead (she spawned in the lake and her collar activated). If she is dead, Kenny will not give you an option to deactivate his collar, instead calling you a "killer" - (Oddly her mother Mrs. Weathers doesn't seem to mind). To rectify this and complete the mission find Sammy's body and resurrect her inside the slave pen, this will allow you to speak to all the Weather's family and deactivate/activate their collars.
Xbox 360 When arriving in Cottonwood Cove prior to starting Left My Heart, Sammy may be standing outside the cage. She will exhibit the same behavior as though she was in the cage.