Just approach to her and be natural, don't try any pua or anything like that, if you think she's interested in you, well that would make things easier.
About what to say, approach to her an mention something that you talked about over facebook or when you are chatting with her on facebook tell her that you are giving her something - a flash drive with music that you both like or a group that you like and you want het to listen as well- these are just examples, do you know what I mean?
Here you have a video that can help you out.
http://www.youtube.com/watch?v=BWeQJmdH ... ature=plcp