As a 16 year-old girl I really wish some parents would just tell their kids to put clothes on because I'd much rather go through my day without seeing some chicks ass. When I was 15 I went through the dressing very revealing stage most girls go through it because they suddenly have a woman's body and they think the only reason they will get a boyfriend if because they look "hot". Personally I would rather cut off an arm then dress like the girl you described but If Idid my mother would tell me to put some clothes on because I'd look like a cheap prostitute.
I went through a stage similar to this at around 15-16, and I also remember my parents being quite disapproving of it and there being a lot of tension in our house. - I'm talking short skirts and minidresses, tight tank tops.. pretty revealing stuff but I didn't think of it as slutty at all. - Bear in mind that it's probably not such a big deal here in australia as the age of consent is 16 rather than 18, which I think is much more appropriate.
I never went through that stage. But when I was sixteen, my mother allowed me to have complete control over what I wore and what I did to my body. Even though she didn't completely agree with what I did i.e. pierce the f*** out of my face etc, she supported me and allowed me to explore myself and my style.
I really appreciated that, and I will do the same for my son or daughter if I had one. But of course, there is a certain line they can't cross.
When I was 15 I loved all the attention I got from the stuff I wore. It was kinda a phase I went though. I remember wearing a super short skirt that was way to small for me and a tight tank top with a red bra. I loved the looks I got then, but now don't think I would do something as daring as that out in public. So maybe that's why she was doing.