Just go up to her with a smile. Then say, "Hi, I couldn't help but notice you and I wanted to introduce myself. My name is Sam."
Hopefully, she will have enough sense to introduce herself and then you can begin a light conversation. In closing, you can say, "I would love to speak with you again." This is her cue to initiate a way she can be contacted. If she is not comfortable with giving out her telephone number, you can ask, "Would it be alright if I emailed you?" "I just want you to feel comfortable."
Best of luck to you.