I am a little confused...

I am in grad school. I ask a classmate, 'Elise', out. Great first date, so so second date. She says she can't date anyone. Two weeks later she invites me to a party. The party was a blast, I stayed at her house. I invited her to another party. I thought she was into me, so did others around me. I ask her out again, this leads to an awkard 180 change in her demeanor, leading her to unfriend me on Facebook. I don't know what I did, I was very careful to avoid the 'nice guy' stuff, I did not creep her out I don't think, we had a lot of fun hanging out and many people told me that we seemed to be into each other. I am quite certian I did not do anything that would merit this complete reversal, because I would have been horrified if I did. I haven't been able to forgive myself for messing up. She then dates another classmate who she eventually complains of being immature and selfish. In January I apologize to her (still trying to figure out what I did), and she unfriends the other guy around this time. Yes, I know Facebook is not 'real' but that seemed pretty drastic. She wanted to send a message I guess.

In Feburary, she likes two things I post on Facebook, once again I understand it's Facebook and I am not trying to read into it, but if she unfriended me she obviously did not want to talk to me then, and you would think given our history she would not want to interact with me at all. I found this to be extremely odd, it was the first time she interacted with me on the site. Being a regular 24 year old guy I make dumb jokes all the time ( I mean not every day, but once in a while), so why now? The likes were within an hour of each other and extremely fast (like the within five minutes of me hitting submit, like she was camped out on my page) , and she was the first grad student to do so.

In March she liked another post, once again the first and only grad student to do so, and commented on another one. A group of us went to a bar one day after class, she was there. She came up to me and had a conversation. I was cordial and polite, but quickly went back to the group conversation. I was later talking to her friend "Rose", and 'Elise' texts Rose asking what I was talking about. I also notice when we are in a group over the past few months she looks at me, or steals glances at me. She will often walk in front of me, like darting infront of me, and linger near my desk for a while in class, not too long but enough for me to notice. Then, a week ago, she says to another mutual friend, “ I know LFCfan1987 is ignoring me, but it won't work to get me back.“ I was stunned by this, I am not ignoring her, why would I go out of my way to make conversation to a woman who rejected me and I mortified myself to? Does this make any sense? And if it is not working...why even mention it at all? Should I talk to her about it, or is there even a point in doing so? I get the feeling if I did talk to her, she would be like OMG why is he talking to me, I really can't say ah hah! you are acting weird, because well, that would be goofy right? What should I do?