Duncan wrote several articles, booklets and pamphlets, especially on issues such as forced removals and pass laws. In the 1970s, she joined the Anglican Church's Challenge Group, a movement that sought to end racism within the church. She also represented the Anglican Church on the South African Council of Churches' (SACC) Justice and Reconciliation Division.
Duncan died at her home in Johannesburg, South Africa, of cancer on 4 May 2010, at the age of 77. She leaves two daughters, Lindsay McTeague and Carey Haouach and two grand children.