How old is this girl, anyway?
Have you talked to her, one-to-one, and explained in clear, non-blaming language that her actions reflect badly on the reputation this band has built up?
Have you discussed that you are concerned with the sexual attention that she is attracting?
Have you asked her what she wants out of her career in music? And where this band fits in with her goals? And what repetoire she would like to do?

(If she wants to do totally different repetoire, you might find her another band to be in. Boredom is deadly to the young, they start sulking and "acting up" all over the place.)

If you treat young people as if they have a brain, sometimes it's amazing how fast they'll grow one...

With respect,
hesperis