Margaret Palmer has written just the one pony book, as far as I know. This one is aimed at the younger reader, and is an absolute charmer. It’s written with a wry humour and the author obviously knows her donkeys and ponies well. Honeypot, the donkey, and Buzz, the pony, are owned by Lucy, and the book contains three short stories about them.
Finding the book
Can be pricey, but ex library copies are usually reasonably priced.