Mavis Thorpe Clark (1909 - 1999) was born in Melbourne in 1909, and died there in 1999. Her first published work was a serial in the Australasian when she was 14, and she published Hatherley’s First Fifteen at the age of 18. She won the Book of the Year Award of the Children's Book Council of Australia for The Min Min in 1966. Her The Pony from Tarella was published by Knight books in paperback in 1977. As far as I know, this is her only pony book.
Pony from Tarella Heinemann, Melbourne, Victoria, 1959, illus Jean W Rowe Knight, Leicester, pb,
When Sandy was on holiday from the orphanage at Tarella Station, he had befriended the beautiful brown mare Sunflower. He hoped to buy her - everyone said she was a one-man horse. But it all goes wrong. When Sandy returns to Tarella, Sunflower has been promised to Phil, and Sandy has to stand by and watch the mare being bullied into obedience.