Don't call me stupid, u have had the best advice and am not following it, who is more likely to be stupid, me or you. I am not trying to insult you (although i dont like ur attitude towards her bf) as i dont care, i was trying to help you.
You know what the best advice is: READ THE BIBLE, it should explain everything. You can also use the search function, i swear i have seen so many very similar questions about approaching girls on track teams.
The gist of all the answers that you will get is to just go up and speak to her. I still have trouble doing it to girls, but what do you lose if she rejects you.
Grab your nuts (metaphorically) and go up and speak to her. The best introduction is hi, my name is . . . whats yours