When I was 20, I had the same thing going on with a 30-something chick in my class. There was mutual attraction, but I was a bit too chicken to make a move (we went on some dates), and nothing ever happened. She seemed somewhat jealous when I finally got a GF, and we never really talked after that.
Honestly, don't feel bad, it wasn't meant to be. Women in their 30s, unless they are somewhat dysfunctional, are pretty much on a different level in terms of needs. You're just starting out your life, and they see you as unstable and someone who could dump them for a much younger woman at any moment. Meanwhile, they are probably looking for marriage and to settle down quickly, especially if they are into their 30s and the biological clock is ticking.
Just think of it as practice, and keep practicing. And who knows, she might get bored or curious and come back into your life. Just be sure to leave it alone for now, don't bug her, and wait for desire to build on her end.