Jean Kinnaird, as far as I know, wrote just the one book under that name, which is a pseudonym for an author who was a 21-year-old university student when the book was published. She lived in Liverpool, but spent most of her holidays riding in Kent, Somerset and Dartmoor. When she was 14, she fell ill and had to give up riding for three years. She wrote to entertain herself: 'I was an only child, and so I used to make up people for myself instead of having real brothers and sisters for company.' Despite her publishers, Lutterworth, declaring on the dustjacket of Finding our Stirrups that the author had plenty more manuscripts waiting to be typed up, nothing else was published under that name. Maybe she carried on under another guise.
Finding Their Stirrups is a good enough read: it shares the same plot device as Diana Pullein-Thompson's Riding with the Lyntons of town children moving with an artistic family to the country, and antagonising the locals. Like the same author's Three Ponies and Shannan, it has wealthy heroines who although occasionally misguided, don’t meet the usual pony books stereotype of the over-monied monster. The conversion of the heroine, Gay, to being a good rider is perhaps a little too pat, but the characters are believable, and the author bangs the drum convincingly for listening to what your pony is saying rather than charging round regardless.
Finding the book
Availability is variable, but the book is generally not expensive when it does turn up.
Dustjacket of Finding our Stirrups