Lenz began working as a child actress, beginning with appearances in three episodes of "This Is the Life" when she was 14. She went on to appear in such television shows as "The Andy Griffith Show" (in the episode "Opie's Group" (1967) under the stage name Kay Ann Kemper) as well as in stage productions. She made a brief appearance billed as Kay Ann Kemper in "American Graffiti" (1973) as Jane, a girl at a dance. She achieved recognition for her title-role performance as the free spirit who captivates William Holden in "Breezy", directed by Clint Eastwood.