She was the middle child and elder daughter of Sir Horace Darwin, through whom she was a granddaughter of the naturalist Charles Darwin (she was born a year after his death in 1882). Her mother, Cecilia "Ida" Farrer (1854–1946), was the daughter of Thomas Farrer, 1st Baron Farrer. Her younger sister Nora, later became Lady Barlow, while her elder brother Erasmus was killed during the Second Battle of Ypres in 1915.