Knudsen made her Broadway debut in My Sister Eileen (1940). She replaced Jo Ann Sayers, who had originated the role of a girl who couldn't decide whether to be an Actress or get married. Finding herself in that situation in real life, Sayers married a naval officer. The show's Producer saw Knudsen working in a stage door canteen and chose her to take over the role.
Knudsen's first marriage was to Adrian Samish, a radio executive. The two eloped after Knudsen's June 8, 1942, performance in My Sister Eileen and went to Media, Pennsylvania, to marry. On June 15, 1949, Knudsen married Jim Jordan. Jr. in Los Angeles, California. They had three daughters together. Jordan was the son of Jim and Marian Jordan, better known as Fibber McGee and Molly. On February 12, 1962, Knudsen married Francis S. Kellstrom, an electrical contractor. They separated that July and were divorced October 22, 1962.
In 1948, Knudsen ventured into a different genre of film, doing comedy instead of drama and leaving Warner Bros. to do freelance work. She also took vocal lessons from Kay Thompson.
In the 1950s and 1960s, Knudsen appeared in guest-starring roles on several television shows. She made two guest appearances on Perry Mason in 1958-1959; one as Sheila Bowers in "The Case of the Gilded Lily," and Marie Chapman in "The Case of the Spurious Sister." Other television appearances included Alfred Hitchcock Presents, The Millionaire, Tombstone Territory, and Pete and Gladys. After appearing in an episode of The Adventures of Ozzie & Harriet in 1965, Knudsen retired from acting.
Knudsen played April Adams in the comedy So This Is Hollywood on NBC (1955). She also had roles in pilots for two programs – Do Not Disturb and Howie – that did not develop into series.
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. Her last film role was in the 1957 film Istanbul with Errol Flynn.
On July 11, 1980, Knudsen died of cancer in Encino, California.
