J.,
My oldest daughter, who is now almost twenty went through this stage. It was a little weird at first for me to see her dress that way. People would stare at her and point, saying things to the other kids and all. I tryed talking to her and getting her to change the way she dressed to help her fit in better, but it didn't work. She wanted more stuff , to make her stand out it seemed, she told me she didn't care what the other kids said. She liked to wear what evwer she wanted, she had the black shirts, pants, and even the "arm warmers" kinda like gloves, they hook over your thumb and pulled them up to your elbows. She had the necklaces the whole nine yards! She dyed her hair many colors, from black to red, blue every color you could think of, it changed almost monthly.
I learned to go with the flow, I even went with her to the store and picked out stuff with her! It really became a fun game with us, and got us even closer to each other. She out grew all of it when she was old enough to get a job, most stores and other places don't hire kids with different color hair. So she stoned it down and went back to the "norm" as everyone seems to call it.
Like I said before, she dresses normal now, not wearing all that dark make up and works at a day care where everyone loves her. The kids , the parents all the other teachers. She is one of the best workers there, all the parents ask her to babysit on the weekends. I don't think you have anything to worry about, sounds like your daughter is a sweet girl, just going through a stage of finding out where she fits in and who she is. I'd let wear what she wants and just stay in tune with her.
Be glad that she isn't into drinking, drugs, cutting or putting herself out there for guys to take advantage of.