I love this movie! Especially because its based on a true story!
It's about a girl who when she was a child was told her mother died in childbirth, the mother was told the same thing about the daughter. So the dad takes her so his girlfriend can't have the girl and raises her. Her dad dies and she was in the hospital after an accident.
So they unite her and her mom even though they never knew about each other. Her mom lives in the country with her boyfriend and has some horses she races (driving).
When they get there they rescued a new horse who name soon becomes Rainbow. They continue to have an inseparable bond even when she is sold. They get her back, but I'll stop there so it wont be spoiled.