I am looking for a 1960-1980 era book, about a girl with amnesia that ends up working on a horse farm, buys a horse from going to slaughter, and then discovers she used to be rich and jumped show horses. Her step parent [I want to say father] ended up being the culprit. The point of view was from the girl, and I want to say the book starts with a car accident, which causes the amnesia.