What would be a good audition piece for Mama Morton (Chicago)?

A friend of mine asked me to help her find an audition piece for Chicago, with the idea of Mama Morton kept in mind. Any suggestions? She can certainly act the part; she has fire, gusto, sass, and can turn up the diva factor, but she isn't as confident in her singing (or dancing really either). So I wouldn't want a terribly difficult song either. I also don't know her voice range, but she's a mezzo of course.