1941
Betty was in the Senior class at school and graduated in 1941.
The girls were broadcasting a regular 15-minute weekly radio show for NBC throughout 1941, titled Dick Roselle and the Brian Sisters. Each week they sang to three of the six popular tunes, accompanied by their friend Dick Rozelle and his quartette.
The San Francisco Chronicle of April 24th 1941 says, of a revue at the Golden Gate Theater, San Francisco:
Song and Dance
A Very Rhythmic Day At the Golden Gate
A Very Rhythmic Day At the Golden Gate
...The other acts in the revue included the three Brian sisters, a blonde, a brunette and a redhead, with voices to match, who harmonized prettily for the citizens - most prettily, indeed, may I add...
Here's a photo of them singing at school in 1941, from the School Yearbook:
Doris, Gwen and Betty in 1941