An army brat who grew up around the world, Billingsley graduated with honors from Fort Smith Senior High School in Fort Smith, Arkansas in 1958.
In 1961, newspapers had her romantically linked with both John Strasberg of the Strasberg Actors Studio dynasty, French director Henri-Georges Clouzot, and French actor Pierre Olaf, with whom she starred in the original Broadway cast of the musical Carnival that had opened that year.
In March 1962, newspapers announced she was going to marry actor Andrew Prine and that she had been replaced in her long-running role in Carnival. However, that May, it was reported that in March, Prine had married actress Sharon Farrell.