Why does she do this?

I attend a community college in my area. I am taking an introductory course in geography, it's one of the requirements, and the class is massive. It's in a huge lecture hall with about 200 students in the class.

So I went to class on the first night and noticed a pretty attractive girl sitting next to me. The instructor wasn't due to arrive for about 20 more minutes, so I decided to try and make some small-talk with this girl. She was really friendly and engaging, so we talked to each other until the instructor showed up.

The instructor introduced the course objectives and said that given the large number of students in the class, it may be best to find a 'note buddy' to get in touch with in the event we ever missed a class. To quote her exactly, she said, 'Turn to that cute guy or girl next to you and find a note buddy.'

Most of the class laughed, including the girl I was sitting next to. She then asked if I'd be her 'note buddy.' She told me to look her up on Facebook, but then gave me her phone number instead.

I obviously was getting ahead of myself by thinking she was interested, though. Whenever I see her around campus outside of class, she ignores me. We text each other sometimes and sit next to each other in class, but that's it.

Any idea why she does this?