Have you got a link to Jill on FB? :)
I read them all...endlessly early 70's
I remember them well, Jill Crewe, Ann Derry, Diana Bush, Mercy Dulbottle, April, May and June Cholly-Sawcutt, and the captain..and some 'insufferable' girl Celia?? Ceclia" Who won everything. Also Val Heath?
Jills Ponies, Black Boy and Rapide and a horse called Blue Shadow rings a bell too! Mrs Darcy who owned the riding school. The Chatton Show.
Fave was Jills Pony Trek where they end up being marooned in a deserted farmhouse where they found lots of hot cocoa to drink and stone hot water bottles....
Oh and Mrs Crosby, the daily-'no relation to Bing'
Poor Mummy, and her hens and hours of sitting typing away at her book about perfect children...and then it all ends with Jill leaving school and training to be a typist....
Its a bit spooky that I can remember it so well, and it was a huge influence on me at 10 years old when my real life was a thousand miles removed from anything even close to Jill's perfect life.