I remember The Black Stallion, but I don't think I read more than one of that series, and I'm no longer sure which one it was. Like @goldenoakfarm I read Marguerite Henry's horse books as well. I think a lot of little girls go through a phase of obsession with horses around age 9-10, and I was no exception. I have never owned a horse, and now I don't want to, because they are big and expensive to own and care for, and I am getting old and tired.