Betty and her older sister, Mary (1916–2015), shared their mother's musical interest and started to learn how to play instruments, such as the saxophone and the banjo, at an early age.

[4] With their father losing his job in the mid-1930s, the Great Depression caused financial difficulties for the family.

As a result, the three sisters entered show business as vaudeville performers to support the family.

As an attempt to bypass child labor laws at the time, both Mary and Joan pretended to be older than they were.

She also appeared in Thank Your Lucky Stars (1943), Ladies Courageous (1944), Cover Girl (1944), Hollywood Canteen (1944), and Too Young to Know (1945).