It doesn't really matter what you say when you approach her. It mostly matters how you approach her. It's usually easier to sound genuine and not-awkward if you have a conversation piece rather than just "Hi I'm ___", unless you have something to say after you introduce yourself. Okay I'm going a bit off topic here actually. Basically, don't stress too much about it. It should be simple. Flirting isn't as much about making the other person blush or laugh or "tingle", it's more about just having fun, so there's really no need to worry about talking to this girl or flirting in general. I'm sure you know how to start conversations with friends. Think of this as the same thing - talk to her like she's your friend and you're having a light-hearted conversation with her. Don't think of it as you're meeting her for the first time, because the only thing anything to do with meeting her for the first time should be introducing yourself - after that, you should be able to talk to her almost as if she was already your friend. Let the flirting come later when you're comfortable with it, cause there's no need to rush either (don't spend a lot of time pretending you just want to be friends with her, though).
I realize all that might be kind of hard to read or understand because I just rambled on a bit and wrote it all in one paragraph. But I'm kinda tired right now and not in the mood to organize it hahaha, so do what you can with it :P. Hope it helped a bit. Lemme know if you have any questions.