Today's pony book is Pamela Cockerill's Winter Ponies, a rarity from the 1980s. The story was based on Pamela's own experiences riding beach ponies she borrowed.
You can read more about Pamela Cockerill here.
Read more about the pony book in Heroines on Horseback, my survey of the world of the pony book from the 1930s onwards. You can buy a signed copy from me (I'll post them worldwide). The book's also available from the usual sources, or your local bookshop.