Allen was born at Stamford Hill, London, and taught to paint by her parents. Her father, Hugh Allen, was a well-known painter himself, and her grandfather was the publisher George Allen (Allen & Unwin). Coming from a very creative family, she began showing her work at the age of 13, and published two books as a child: A Child's Visions and The Birth of the Opal. She painted and drew fairies and religious subjects, and worked as an illustrator for many magazines, including The Illustrated London News, The Sketch, and The Tatler.
Apparently her precocity caused a sensation in London. Anthony Ludovici was not pleased, declaring in The New Age (October 9, 1913; 13:24:704) "She did go on and paint reasonably well, working in stained glass as well as drawing and painting". The newspapers in 1913 made much of time she spent in St Ives, under the headline 'The Celebrated Child Artist at St Ives', saying that she had become a familiar figure on the beach that summer. In London's Daily Mirror this 'news' accompanied two pictures of the artist and her sister on St Ives beach. She employed one of the Island studios, for a period, in St Ives.
Her work had a strong religious and spiritual element, and she completed pictures on site in a series of churches. [See Spirit of the Ages website for a selection of religious art]. She lived for many years in Chalford, Gloucestershire.