April Jaffé wrote two pony books. Her first book, Satin and Silk, was written during school holidays when she was fourteen years old. The book was based on fact, and it was 'the trust and devotion which grew between her pony, Satin, and herself which provided the inspiration for the story.' Her second book, The Enchanted Horse, is notable for the fact it was illustrated by Charlotte Hough, whose lively illustrations graced several pony books.
Finding the books
Satin and Silk is reasonably easy to find, and is cheap as long as you don’t want a copy with a dustjacket. The Enchanted Horse (often confused with the much later title by Magdalen Nabb) is very hard to find indeed.