Born in England of Grenadian and Jamaican parentage, McKenzie lived between 1975 and 1981 in Grenada, where she attended St Joseph's Convent and the Institute for Further Education.
[6] In 1981 McKenzie was employed as a Treasury clerk in the Ministry of Finance, Grenada, then between 1983 and 1985 she worked as a civil servant in the British Department of Health and Social Security, and from 1986 to 2005 she held various positions connected with community relations, including as a race equality officer in the Hackney Council, studying at night school for a law degree.
[4][7] During a 2012–2014 sabbatical, McKenzie was chief executive of the female prisoners welfare association, Hibiscus Initiatives, heading a team of professionals doing advocacy and support work with ex-offenders.
[9][10] For years before the harsh effects of the government's hostile environment policy gained national media attention, McKenzie had been helping Caribbean-born Britons and other migrants to prove their right to stay in the UK, where they had come to live decades earlier but had been provided no official documentation.
[11][12][13] Her work since 2018 has become increasingly focused on compensation claims linked to the Windrush scandal,[14] and she has represented more than 200 of those wrongly classified by the government as illegal immigrants,[4] whereas "They felt they were moving from one part of the Commonwealth to another!
She was aware of the looming Windrush scandal long before it got its name, and her frustration over the continued delays to justice is fuelled by a memory of the years she spent trying and failing to get officials to pay attention.