While Mary Louise Zeyen was born in Washington State in 1926, her family moved to the Los Angeles area when she was very young. She performed with her sisters Terese (piano) and Margaret (violin) as a trio in concert and on radio. Her talent on cello was recognized at a young age, and she became a member of the Peter Meremblum California Junior Symphony Orchestra, one of the premier youth training orchestras in Southern California.

Zeyen was a frequent background player in various movies during the 1930's and early 1940's, including bit roles as a young cellist in the Goldwyn film "They Shall Have Music" (1939), and "There's Magic in Music" (also known as "The Hard-Boiled Canary") (1940) as an unnamed cellist in the camp orchestra. She was also in the Meremblum orchestra in a short subject "California Junior Symphony" (1942) in the film "Song of Russia" (1944).

In 1947, she followed sisters Terese and Peggy, and took the vow as a nun in the Sisters of the Immaculate Heart of Mary (IHM), with the name of Sister Mary Anthony. The three performed as the Immaculate Trio for many years. She also was a member of the Los Angeles Philharmonic for several years, until arthritis forced her into retirement.

She spent her later years in retirement in Southern California.

She died March 14, 2013, in Pomona California.