Rosemary's father Hugh had been married three times. In 1913, he married Marion Atkinson, with whom he had two sons, William Cecil Alexander (1914-1916) and Edward Alistair (1915-1969); they divorced after World War I. In 1924, he married the children's writer Enid Blyton (1897-1968), with whom he had two daughters, Gillian Mary (1931-2007) and Imogen Mary (b. 1935), they divorced in 1943. The same year, her father married the romance writer Ida Crowe; Rosemary was born the following year, and was to be their only child.

A veteran of World War I and assistant to Winston Churchill, her father was also editor of the book department in the publishing firm of George Newnes, but in 1950, had to file for bankruptcy after his dismissal. In this time, her mother published romance novels under several pseudonyms, being in print with several major international publishers at the same time. During Rosemary's childhood the family travelled widely and lived in many parts of England.

She contacted her half-sisters after Enid Blyton's death, but their father never saw them again; he died in Malta in 1971.

Rosemary wrote nine romance novels from 1969 to 1981, and now helps her mother with some of her many projects. In 2009, her mother published her autobiography, Starlight.

Novels

• A Touch of Starlight (1969)
• The Mountains of Spring (1971)
• Song Above the Clouds (1972)
• Saffron Sea (1973)
• Summer Comes Slowly (1976)
• Tiger in Darkness (1978)
• White Hibiscus (1979)
• The Breadth of Heaven (1981)
• The Sun and Catriona (1981)

Anthologies in collaboration

• Mountains of Spring / O'kiss Me, Kate / Blue Jasmine (1976) (with Valerie Thian and Violet Winspear)
• Sea Lightning / White Hibiscus / Liberated Lady (1987) (with Linda Harrel and Sally Wentworth)