Frieda K. Brown
Full name Frieda Kenyon Brown. American author. Seems to have just written the one horse story which is based on a real life incident in her childhood. She continued her devotion to rescuing horses into adulthood by running a rest home for retired and ill-treated horses.
If looking for the book on internet bookshops it is worth searching under F. K. Brown as well as the other two variations of her name, as books seemed to be filed under all three.