A medical doctor and author, Fischer Williams was the daughter of the Sir John Fischer Williams, an international lawyer, and Majorie Fischer Williams, an artist.
Growing up between London, Paris, and Cornwall, her family home was Lamledra House near Gorran Haven. Her sisters were Prue Fischer Williams, Judith Hubback, a sociologist, and Jenifer Hart, a civil servant married to the legal philosopher H.L.A. Hart.
She gave wartime service as a nurse, then studied to become a neurologist in Paris, Edinburgh, London, and Oxford. Fischer Williams moved to the United States in the late 1950s and married Patrick Werner, an American, in 1974. After they both retired they spent half of the year in their home in Milwaukee, Wisconsin and half at Lamledra.
Fisher Williams authored several textbooks and medical papers as well as the book Emotions of a Physician, published in 1993. She was fluent in French and was an accomplished musician, playing the violin.