OK, so to the OP... and not to belabor the point, but...
If this chick singer is under so many restrictions with regard to showing her picture, etc., how are you marketing her as part of the band at all? I mean, if her biggest asset to the band is that she's hot, but you can't capitalize on that in your promotion, what's really the point? On top of which, I have to think her age is precluding you from playing bar gigs (which are the bread-and-butter of most cover bands I know, anyway). In which case, she is a significant liability to your band irregardless of how good she looks and/or sings. Or is she one of these teenage girls that looks 25 and so none of the venues you play raises the issue?
I'm not a lawyer and don't know your local statutes but it feels to me like if you're (not personally, but as the band) bringing her into bars to do gigs, you are technically open to charges of contributing to the delinquncy of a minor or some such.