This is one of seven books, which comprise the Jill series by Jemma Spark .
They're a follow-on of the original Ruby Ferguson Jill books, which were the most popular pony books of their time and translated into many languages.
Ostensibly, they are classified as Young Adult, and contain no explicit adult content.
However, they fit more neatly into a developing genre with a devoted following called 'Pony Books for Adults'.
They are set in the early 1960s and contain little nugge.