When you say that you've studied with INFP, what did this entail? Did you talk to each other at all? How did the studying come about? I would have to understand what kind of exchanges you've had so far to feel good about giving my opinion on how you should approach her. Direct is nice, but totally out of left field AND direct can throw someone off, specially shy INFP.
The good thing is that most INFP's can extract quite a bit from minimal interaction, enough to fill their heads for days. The bad thing is that if your INFP has done this and was then confronted with a reality where she made herself more available to you and you not only didn't take the opportunity but also spent the night chatting up ENFP, it could be a harsh blow. She may have mentally put a break on any potential you had. I'd provide new info to her that shows you are still interested, and pretty quick like Marmie said.