Hi, everyone! New to the forum. I've been lurking around, watching these responses. I know the reason no one's suggested her is that she's technically "too old," but damn, I think Kay Hanley would be a great Sally Bowles. She's definitely capable of reading much younger than she is, and she'd bring a nice edge. (She & AFP have even already worked together, though maybe that means that if Amanda thought she'd be a good fit, she'd have asked her.)
I also think Emilie Autumn might be interesting. She doesn't have much in the way of acting experience per se, but she certainly has a very theatrical energy.
And I like the Amber Benson suggestion, too, even though her voice might be a bit on the high side for Sally.