Here's the thing. If you could handle just seeing her once in a while, and not get upset when she flakes, and have no expectations, and not worry about when you will see her again...keep doing what you are doing.
But, obviously, with as much time as you think about her, talk about her, write about her here, it DOES BOTHER YOU that she isn't more available to you. You would like more, but for whatever reason right now she doesn't.
You have one shot, and its a win win situation. Quit her cold turkey. No more getting online and talking to her. No more emails. No more phone calls or texts. No more going out with her and hanging out. Give that a couple of months. IF she contacts you asking you out, say you are busy. Not only will this make her realize what she is losing IF she really likes you, but it will also enable you to start moving on, date other people, and stop thinking about her. If after that she really wants to be with you, trust me she will make it abundantly clear to you, and you can go from there.
Good luck!