Annie is a fellow hunter who knew Sam, Dean and Bobby Singer, she had been sexually involved with all three of them (with Sam when he had no soul). Annie investigates a haunted house after she receives a call from a ghost there asking to be freed. Annie decides to call Sam and Dean in as she heads towards the house. Once there, she discovers the bodies of a murdered couple, and moments later she is killed herself. Annie becomes a ghost but is determined to solve the case. With fellow ghost Bobby, the two figure out what is going on and help Sam and Dean figure it out with the help of another ghost.
After the case is solved, Annie is given a hunter's funeral and is put to rest. While she and Bobby believed this would send her into oblivion, the later revelation that ghosts that are put to rest are taken to their true final resting place, she is presumably now in Heaven.