The Bad Wolf and the Girl Who Waited
Amy would never know what happened to her friend Rose. They'd met when they were little and both in therapy over a man called "the Doctor". Rose said he helped her with her homework; while Amelia swore he'd take her through time and space. No one ever believed the girls, but they believed each other.
Then came the day of the mannequin invasion and Rose disappeared. Jackie never even knew about Amy so no one ever told her that Rose was safe. The day the Battle of Canary Warf occurred Amy saw the name Rose Tyler on the list of dead.
If the Doctor was real he would have saved Rose; Amy knew that. So that was the day Amelia Pond lost faith in her magical Doctor.