I'm sure the feelings you have are real.
What concerns me here is that if she's in fact dating a senior, why is she flirting and touching you? To me that would indicate a problem in her relationship with the senior. If she's actually with this person, she shouldn't be doing this to him. Do you know for sure if she's with him still as a girlfriend or are they just friends? This needs to be sorted out before the next step is taken on your part.
If it's the latter, perhaps it's time to just go ahead and ask her if she'd like to go out to a movie, coffee or a track meet with you.
