Horse & Pony Books:
THE GRAND ROGUE
(DODD MEAD [USA] 1958)
SUMMARY: A girl buys a rogue horse at auction. Can she reform him?
(WESTMINSTER [USA] 1960)
SUMMARY: Not to be confused with the ubiquitous doll of the same name! When Barbie wins a Shetland pony, it is the start of romantic entanglements with two very different young men.
I am not sure if these were every reprinted. Both books are hard to find, even in America, The Grand Rogue extremely so.