Horse & Pony Books:
APPLEGATE: THE STORY OF A GIRL AND HER PONIES
(1st edition YOUNG WORLD 1972)
ILLUSTRATED BY MICHAEL WHITTLESEA
Possibly reprinted in paperback.
SUMMARY: Young adult read. Madge inherits a riding school called Applegate, a dream come true for any pony mad girl. But the reality of a run down set of ramshackle stables and inhabitants is far from the dream...
PONYMAD RATING: 2-3 HORSESHOES
Reasonably easy to find in the UK and not usually expensive, harder to find elsewhere. It was possibly reprinted in paperback but I am still trying to confirm this.