[2] Knudsen made her Broadway debut in My Sister Eileen (1940),[3] succeeding Jo Ann Sayers, who had originated the role.

(In a February 15, 1948, newspaper column, entertainment writer Louella Parsons quoted Knudsen saying, "My first picture was Shadow of a Woman with Helmut Dantine.

[2] That same year, she appeared in bit parts in several films including The Big Sleep and Humoresque with Joan Crawford.

In 1948, Knudsen ventured into a different genre of film, doing comedy instead of drama and leaving Warner Bros. to do freelance work.

[2] Despite appearing in big budget features with established stars, Knudsen's career never took off and she was relegated to smaller roles in B movies.

[5] Knudsen played Lois Graves in the radio version of Junior Miss,[6] Karen Adams in Woman in White.

Other television appearances included Alfred Hitchcock Presents, The Millionaire, Tombstone Territory, The Life and Legend of Wyatt Earp (as 'Kansas Lily'), Pete and Gladys and three times on Bat Masterson (as "Louisa Carey" in 1959, as "Katie" in 1960 and as "Lottie Tremaine" in 1961).