The great-great-granddaughter of the surgeon William Marsden, she trained in art schools of London before earning employment sketching portraits of motion picture personalities.
[2] Her first job was with a small advertising agency, where she sketched portraits of motion-picture personalities from publicity photographs,[1] which were displayed in cinemas for promotional purposes.
[2] Resisting pressure from her family to return to England,[2] Sandwith hitchhiked along the Birdsville Track, a cattle route linking Queensland and South Australia, between August 1952 to February 1953.
During her journey, Sandwith sketched the Aboriginal peoples, sheep shearers, landladies, and fellow travellers,[1] mostly in pencil but occasionally in pastel.
[4] The journalist of The Sydney Morning Herald wrote that Sandwith had realised she "stumbled on a part of the world that had never been adequately documented" and her work became "an incredible record of the harsh outback landscape – and the characters, white and black, who called it home.
[3] In 1954, she persuaded Sālote Tupou III to sit for a portrait, the first of a queen of Tonga,[2] after a cabinet meeting of Tongan nobles convened to grant her permission for the painting.