No back away and stay away from her. I think some times people don't know why they act the way that they do and trying to find out will just aggravate them, and you.

I had a weird similar experience yesterday. A co worker came up and wanted to learn how to take the subway. I even left early to show him. But when we got in the subway his entire demeanor changed. Like suddenly he was incapable of joking or even not clearly looking like he was disgusted by the whole thing (and me). It was like Dr. Jeckyl and Mr. Hyde. I was highly offended by it. I just decided that I have to keep my door closed more often... people don't seem able to stuff down their feelings at the moment for manners.