Manwaring attended the University of British Columbia in the 1970s, and was a member of the UBC Young Socialists. A steelworker by profession, she has been a member of the Canadian Auto Workers Local 707 in Oakville for several years and remains a member in good standing as of 2006. She was thirty-seven years old in 1988. She campaigned in favour of a shorter work week, affirmative action programs, and the cancellation of Third World debt. She received 123 votes (0.31%), finishing sixth against Liberal candidate Joe Volpe.
Manwaring was an occasional contributor to the RWL's newspaper, Socialist Voice, in the 1980s, and later wrote articles for the newspaper of the Communist League, a successor party to the RWL. She was interviewed for an article on Canadian women in non-traditional occupations, printed by Labour/Le Travail in Spring 2006.