Janice Gray is an author about whom I have been able to find out very little:  a Janice Gray was writing romances for Mills and Boon at about the same time A Credit to the Family was written, but I have not been able to find out if the two authors are one and the same.

Finding the book:  It is extraordinarily difficult to find.

Sources and links:

British Library catalogue

Thank you to Lisa Catz for the photograph and information on the book.

Janice Gray

A Credit to the Family

Max Parrish, London, 1965.  144 pp.

“Nikki was sent to stay with her cousins on a stud farm in Gloustershire. A promising ballerina, she is terrified of
horses and afraid that she will be forced to ride. Her cousins, Sally and Tim Carleton, are both excellent riders,
and do not understand this city-bred cousin who is afraid to ride. It is unheard of for a Carleton to not ride. They
feel she is a disgrace to the family. But Nikki is not as feeble as she appears to them. Secretly she continues
with her ballet, and eventually she gets the chance to prove her worth and win the respect of her horse-crazy
cousins. Along the way, she also learns to love horses.”
 

Bibliography - pony books only