After completing her schooling at Roedean in Johannesburg she studied literature at Oxford University from 1922 to 1925. Sumner later studied painting at the Westminster School of Artist Attracted to the French art scene, Sumner moved to Paris in 1926, where she studied for four years at the Academie de la Grande Chaumière.
Although she had been separated from the South African art world she invited by Walter Battiss to exhibit with the New Group in 1938. She was awarded the by the Suid-Afrikaanse Akademie vir Wetenskap en Kuns in November 1971, accompanied by a sensationally successful "semi-retrospective" exhibition at the South African Association of Arts Gallery in Pretoria. During her stay in Paris in 1978, she was diagnosed with Guillain–Barré syndrome, Sumner died in early January 1985 at her home in Melrose, Johannesburg.
