Molesworth Allen suffered tuberculosis, polio and cancer as a child and spent most of her childhood in hospitals and unable to attend schools.
[5] During World War II Molesworth Allen volunteered for the Women's Auxiallary Air Force, before replacing Cranwell as botanist at Auckland Museum from 1944 to 1947.
[5] In these years she made important additions to the museum's collections, including mosses and sedges and the field notebooks of T.F.
[1][5] From 1948 she travelled extensively in Southeast Asia, particularly to Malaysia, Borneo and Thailand, observing plants and collecting samples from the jungles.
[1] In 1963 Molesworth Allen retired to Los Barrios in Andalusia, Spain, where she continued to collect and study plants, particularly ferns.
[1][3] A part of the Gua Tempurung, the largest limestone cave in Peninsular Malaysia, is named the Molesworth Allen Tunnel after her.