[2] Encouraged by her mother and grandfather, she landed her first professional role in an episode of The Doris Day Show in 1968.

[3] Gerritsen appeared in several episodes of Gunsmoke, which helped to land her first regular role as Lydia Monroe, the precocious daughter of William Windom's character, John Monroe, a Thurber-like writer and cartoonist, in the 1969 NBC comedy series My World and Welcome to It.

Also starring Joan Hotchkis as Ellen, Lydia's mother, the somewhat dark situation comedy was based on the cartoons and comedy of author James Thurber, combining live-action storylines of family strife and social satire with animated cartoon characters that broke into the frame during segments featuring Monroe's daydreams and fantasies.

Bess was a recurring character throughout the length of the series and Gerritsen continued playing the role in the spinoff, Phyllis.

She also appeared as Linda in The War Between Men and Women, starring Jack Lemmon and Barbara Harris.