As a kid I ate, slept and drank horses. And almost every book I read was about horses. I don't remember the exact details of this story, but of the many horse books I read, Jean Slaughter Doty's were among my favorites. If you have a girl with a horse obsession this would be one of my first recommendations. I think I identified with her characters more deeply than I did with Walter Farley's and others'-- great as many of those books are. Young girls have this intensity of passion for their horses- a powerful emotional connection- and she mirrors that for them in her characters.