Welcome Home, Roxy Carmichael
Dinky is 15 years old and is a social outcast, basically. She is also adopted. A movie star is coming to town and Dinky thinks she's her daughter. She's an outsider and her own adoptive parents don't want her;they are going to put her in some kind of mental facility.
Lots of the kids make fun of her. There is one boy, though, that wants her as his girlfriend. On the other hand there's an adult guy that wants to take Dinky out of the school and put her into a school that is for trouble-makers and those with learning difficulties. Yet Dinky has been getting straight A grades since elementary school.
Dinky has a friend in the school's counselor. The guy that had a kid by Roxy when he was younger finds out it is causing problems in his marriage. Dinky believes that she is that child they had.
Reality, though, isn't always what we expect it to be. Yet, sometimes, a someone special shows up when we least expect it.
A good movie.