After arriving in California in 1948, Leah studied for three years with Dennis Weaver's workshop for actors. Her first tutor was Mme. Maria Ouspenskaya.
In reflecting on once being fat, Leah reported in a Richmond newspaper that in the early 1950s she put on unwanted pounds while she and her husband were in England. Bill Schallert was on a fellowship, and to occupy her time Leah ate. Back in America, despite their tight budget, she became a compulsive eater. To return to her slim figure Leah developed a plan to lose three pounds a week. The plan had to be inexpensive and healthy. It consisted of three times a day eating a broiled hamburger, a glass of skim milk, an orange, and raw carrots.
She appeared with her husband William Schallert in two episodes of The Patty Duke Show (1963), in which he played Martin Lane.
In the late 1940s Rosemarie D. Wagner was a registered Democrat on the Burbank, California Voter Registration List for Los Angeles County, California, USA.
William Schallert and Leah Waggner were both in the cast of the 1948 Circle Theater production of "Rain" in Hollywood, California, USA. Circle Theater used what was termed Unique Circle Players staging where the actors perform in mid-room with the audience seated in a semi-circle to create intimacy and realism. In "Rain" the audience was in a trader's house living room under a bamboo roof and rain effects. It was designed to simulate a dismal Pago Pago Island setting. The play, which opened on October 24, 1948, cast Mr. Schallert as the Rev. Alfred Davidson, a young pastor experiencing moral and spiritual conflicts with his wide, Sadie, played by June Havoc. Miss Waggner was cast as the wife of Dr. MacPhail. The Unique Circle Players were amateur actors and actresses.