I like aries’ advice. Go up to her and start talking with her. She is not expecting you to go up to her. She will feel awkward if you approach her, especially if you are nice to her. Take charge of the conversation and show confidence. Ask her for her name, where she goes to school. In other words, turn the table – you get info about her. Make her feel hunted.
One time I was at an ATM getting money when two guys who were talking behind me, then they separated a few feet. One was at 4 oclock and one at 8 oclock. It felt that they were ready to attack. Without saying anything, I looked at them and made them realize that I am not unaware of their tactics. It was enough to stand them down. After I left and walked a half block, I realized that I forgot the receipt. I went back to the ATM and they were still there talking, not expecting me. I barged past them, said “excuse me”, and grabbed the receipt. They were not expecting it and they seemed a bit startled.