Mary Sharp has writtten two titles for the J A Allen Junior Equestrian Library. She was born and educated in Oxford; rode first on Port Meadow, and ran a sailing school in Cornwall with her husband. Her sailing background is reflected in Dream Horse, whose heroine, Becky, is the only horse lover in a family of boaties. Second Best Pony is unusual in featuring a Fell pony: not the commonest breed to crop up in pony books (though nowhere near as rare as the Dales – none, as far as I know.)
Finding the books
Both easy to find.