Knowles was born in Fort Dodge, Iowa. Her father was an orthopedic surgeon who invented the Knowles pin, a medical device still used in pinning some hip fractures.
She attended St. Mary's College of Notre Dame and later received her bachelor's degree in languages from the University of Iowa. She worked as a Spanish translator after graduation.
She worked for a firm in the mining industry in Cleveland, and then came to the Chicago area in 1974 at the invitation of a cousin, Hugh Knowles, to join the electronics firm he founded.
With no knowledge of the subminiature electronic hearing instrument components manufactured by Knowles Electronics for hearing-aid manufacturers, she started in new product development.
In 1979, she married Hugh Knowles and eventually became vice chairman of the company. After her husband died in 1988, she became chairman, a post she held until the company was sold to a private equity firm in 1999. Since 2005, the Itasca-based business has been part of Dover Corp.
She continued to lead the Knowles Foundation, which supports the arts, education, health, international development, and social services.
Her involvement with Lyric began when she became a Lyric Opera donor in 1990. She was a member of the Lyric's guild board of directors from 1993 through 1999.
In addition to Elmhurst Hospital, she contributed to other area health care organizations including the Shirley Ryan AbilityLab, formerly the Rehabilitation Institute of Chicago, and Loyola Medical Center in Maywood.
Survivors include the daughters of Hugh Knowles, Margaret and Katherine; eight step-grandchildren, 11 great-grandchildren; and three great-great grandchildren.
A second marriage ended in divorce.