From 1943 to 1946, Cecily studied art at Witwatersrand Technical College Art School in Johannesburg, under Maurice van Essche. Followed by study at Chelsea Polytechnic (now Chelsea College of Arts) in London, under Henry Moore; and Camberwell School of Art (now Camberwell College of Art) with Victor Pasmore. In 1954, Sash received her fine arts degree from University of Witwatersrand. After graduation she briefly taught at Jeppe Girls’ High School in Johannesburg. Shortly after she started teaching at the University of the Witwatersrand, where she remained until the 1970s. In 1965, she was awarded an Oppenheimer grant in order to further study arts education in Britain and the United States. In 1974, Cecily moved to Britain, where she settled in the Welsh Marches.
Sash was primarily a painter, and a printmaker but she also worked in mosaic and tapestries. Sash painted many South African murals that were commissioned, including at the Transvaal provincial administration building in Pretoria; the University of the Witwatersrand; and the Transvaal Institute of Architects.
She was part of the Amadlozi Group founded in 1961. The name “Amadlozi” (Zulu: ancestors) was used for a conscious appropriation of African sculptural traditions. In 1965, Sash was included in the seminal South Africa artists’ exhibition at the Grosvenor Gallery in London.