Her parents, Arthur Walder and Millie, née Bowen, were part of a prominent and wealthy family; her uncle Sir Samuel was Lord Mayor of Sydney in 1932 and later served as a United Australia Party member of the New South Wales Legislative Council.
In 1952 she married Royal Navy officer Michael Kersey, and moved around with him to Scotland, Malta and New Zealand; on his retirement, they settled in Armidale to manage a grazing property.
There Kersey became involved in organisations such as the Save the Children Fund, Family Planning, and Zero Population Growth, and joined the Australia Party, forerunner of the Australian Democrats.
[3] After her separation from her husband, Kersey moved back to Sydney and became involved in the nuclear disarmament, women's rights and conservation movements.
A member of the New South Wales Council for Civil Liberties, the Australian Drug Law Reform Foundation, Amnesty International, Justice Action, the Friends of the United Nations, and Community Action Abroad, her activism continued into her 70s and 80s, campaigning for a republic and a carbon price and against the Iraq War and the treatment of refugees.