We also had the book by same author, Sea Star, Orphan of Chincoteague. There was a third, Stormy, Misty's Foal and one more, Misty's Twilight.
You’d likely enjoy Black Bess and the ride of Betsy Dowdy then. It’s generally not held to be fictional though.
http://www.womenhistoryblog.com/2009/05/betsy-dowdy.html