[5]: 314 She was the eldest of five children, one sister and three brothers, and attended the Roedean School in Johannesburg where the principal, Ella la Maitre's religious and liberal views would influence Duncan's life.
[4]: 76 [5]: 313 During her youth she spent some time in Southern Rhodesia before leaving for Scotland where she was educated at the Edinburgh College of Domestic Science, qualifying in 1953.
[5]: 313 [6] On her return to South Africa she married architect Neil Duncan in 1955 and the settled in Southern Rhodesia where she worked as a teacher of domestic science.
[3][6] They stayed there for eight years before returning to South Africa in 1963 and joining the Black Sash and would be the chairman of the Transvaal region.
[4]: 77 Her religious work included issues concerning justice and peace within the Anglican church and non-violent direct action and would become one of two female canons, prior to women being ordained as priests in South Africa, as Canon of the Cathedral Church of St Mary the Virgin in Johannesburg.