 Born in London, England, Trimmer emigrated to Toronto with her husband Douglas in 1954, where they settled on the Toronto Islands.Working as a secretary and then a business and typing teacher at Victoria Park Collegiate Institute, Trimmer became interested in politics after opposing development in her community on the Tam O'Shanter golf course lands.After successfully leading the movement to block the development, Trimmer stood in the 1974 municipal election for the position of controller, and was elected.