She was elected to Scarborough municipal council in 1978 and served for 10 years as an alderman. In 1985, she was one of the alderman chosen by Scarborough Council to sit on Metro Council and in 1988, she won a seat in her own right on Metro Toronto Council from the ward of Scarborough Wexford. While on Metro Council she served as Deputy Chair under Alan Tonks and also served as Chair of the Board of Governors of Exhibition Place. She ran for Mayor of Scarborough in 1994 coming in third place behind Frank Faubert and Marilyn Mushinski.
In 1995, she was chosen by the Ontario NDP government of Bob Rae as one of the province's appointees to the Metropolitan Toronto Police Services Board with the intention of having her succeed Susan Eng as chair. She was elected Chair by a 5-2 margin.
Prinsloo's term as chair saw improved relations between the Board and the Metropolitan Toronto Police compared to the tempestuous relationship that existed under Prinsloo's predecessor, Susan Eng.
Following the 1997 municipal election that saw City Council move to the right under new Mayor of Toronto Mel Lastman as well as the more conservative tenor of the province's appointees to the Board under Conservative Premier Mike Harris, Prinsloo was challenged for the position of Board chair by conservative Councillor Norman Gardner, despite the long-standing convention that an incumbent chair is not challenged for the position and that the chair of the board not be a sitting city councillor. With Lastman's backing, Gardner, won the position by a 4-3 margin.
Prinsloo died on December 2, 2017, aged 79, at a Toronto palliative care facility after being diagnosed with brain cancer.