Helen Barrett was born in 1942, in Hindmarsh, South Australia, She worked in publishing and journalism and taught at Presbyterian Girls’ College. The State Library, South Australia picks out her books for special mention in its survey of equestrian literature. They are “evocative of our long, hot summers and follow with humour the lives of teenagers and their friends, families and horses. Readers, especially South Australian, can enjoy descriptions of the Royal Adelaide Show, holidays at Victor Harbor, and long drives into townships like Burra to do the shopping and collect the mail.” Helen Barrett also wrote under the name Elizabeth Whitbread.
Thanks to Adele Kirby for telling me that the two mystery books mentioned on the internet, A Good Reason for Riding and A Good Event For Riding were not finished because of Helen's early death.
Finding the books: the Helen Barrett books are not impossible to find, but are expensive when they turn up. The only Elizabeth Whitbread book that seems to turn up with any regularity is A Good Year for Riding.