Clarke was born in Tasmania,[1] one of eight children of Charles McLachlan,[1][2] a merchant in Hobart and a member of the Tasmanian Legislative Council, and his wife Isabella, née Dick.
[2][3] Charles McLachlan's work took him to Britain during Margaret's childhood,[3] and she was educated in England,[2] becoming proficient on the harp.
[2] Clarke married her first husband, Captain John Lunan Wilkie of the 12th Regiment of Foot[1][4] on 22 April 1856, at St David's Cathedral, Hobart.
[2][4] She had inherited about £3,000 on Wilkie's death,[2] and "it was her favorite study to seek for all who were in trouble or poverty, and relieve their necessities to the utmost of her power.
[2] There, she helped to establish the Home and Training School for Nurses for the Sick,[1][2][10][12] and donated £150-£200 per year to the Sydney City Mission.