Winsor was raised in Berkeley, California. At the age of 18, Winsor made a list of her goals for life. Among those was her hope to write a best-selling novel. Winsor graduated in 1938 from the University of California, Berkeley. During her school years, she married a fellow student, All-American college football player Robert Herwig. In 1937, she began writing a thrice-weekly sports column for the Oakland Tribune. Although that job only lasted a year, Winsor later returned to the newspaper to work as a receptionist. She was fired in 1938 when the newspaper chose to trim their workforce.
Winsor became interested in the Restoration period through her husband. Herwig was writing a paper for school on Charles II, and, out of boredom, Winsor read one of his research books