Florence Hayes (1895 - ) wrote several children’s books, some of which have an American Indian theme. As far as I know, she wrote two horse books.
Finding the books:both titles are reasonably easy to find. Neither had a UK publication.
Links and sources Terri A. Wear: Horse Stories, an Annotated Bibliography, Scarecrow Press, 1987
Bibliography - horse books only
The Burro Tamer
Random House, New York, 1946, 209 pp, illus Manning de V. Lee
“Ricardo tries very hard to tame the wild little burro he rescues from the quicksand so that he can sell burro rides and ride in the parade at the fiesta.”
Chee and His Pony, the Story of a Navajo Boy
Houghton Mifflin, Boston, 1950, 262 pp, illus William Moyers
“Chee ends his second year at the Navaho school and eagerly awaits the pony his grandfather promised him, but he learns that his grandfather doesn’t even have enough money to replace his own two old work horses.”