Callie was poisoned by her step-mother with bleach when she was eight, and has remained in a vegetative state since. Her father, Dr Garrison keeps her alive, and reads her Fairy Tales. Increasingly frustrated that her father won't let her die, and doesn't know the truth, she lashes out, causing a series of deaths based on the stories he reads her.
When Dean sees Callie, who is obviously a spirit, she indicates that she was poisoned by her step-mother by leaving behind an apple. Sam has to convince Dr Garrison of what Callie is doing, and when he finally accepts the truth, Callie's spirit is at rest.