From Wikipedia article:

Minnie the Moocher defined Betty's character as a teenager of a modern era, at odds with the old world ways of her parents.

and later,

Officially, Betty was only 16 years old, according to a 1932 interview with (creator, Max) Fleischer (although in The Bum Bandit, she's portrayed as a married woman with many children, and also has an adult woman's voice, rather than the standard "boop-boop-a-doop" voice). ,

so maybe MGM's chip portrays the later Betty?