She is 18 and has seemed a bit upset lately,I asked her what was wrong and she finally told me she was molested by someone when she was 3 and a half, she remembers it and what they where wearing but can't tell me who it was because she has "blocked out the face" is that possible?I'm vary confused right now because she has been home schooled her whole life and never been left with anyone!there was a neighbor who knocked on our door late when she was 3 and he said he was in love with her and 'mentally connected' we moved because of that shortly after(he was always in and out of mental hospitals) but there's no way he could have gotten in her room.the only other person it could have been would be my ex-husband,other then his brother getting in trouble for 'tickling' his own daughter, there's nothing that would lead me to believe it would have been him and we don't speak anymore so I won't be able to talk to him about it.
Is there any way we can prove that this happened?is there hypnosis to remember who it was?she said she has always remembered it but lately has been having 'flashbacks' and reliving it, witch is what's bothering her.

She should see a psychologist first, who can determine if she is a candidate for hypnosis. It's important to let memories proceed at her own pace, and not being able to see a face protects her for now. That is, if this is a genuine memory. There's a slight chance that it seems real to her but is made up of what she has read and seen, along with unusual actions of people back then that are real.
But with the neighbor... I'd give it serious weight.
No one can say it was 'impossible' for anyone to molest her. There is always some way, through a window, outside playing, someone fell asleep...

She does need professional help, first this may ( or may not be real) at that age, what she thinks she remembers may be something totally different, and other events could be confused in her mind.