Fiona Citroen wrote this book when she was 24. As far as I know, she wrote nothing else under this name. The book is one of the last pony books to be published as a hardback with dustjacket: it became progressively the norm in the 1970s for books, even for sure sellers like the Pullein-Thompsons, to be issued first as paperbacks.
Finding the book
Easy to find and usually reasonably priced.