Help! Is this person really two-faced?

I know this coworker, which I find her to be an extremist. Some days (when I am working with her), she acts friendly, pleasant, chatty, charming around me when I am being kind to her like giving her a ride to work and home, and being a reliable person to her when she needs help. I found her company very enjoyable. We got along very well and we were talking like great friends. We felt very comfortable and compatible with one another. All of a sudden, the next time I see her at work in the office, she doesn't even say hello to me when I believe she saw me first. She acts totally different, as if I am not there. Minimum conversation or even awkwardness persist when we do talk. Sometimes she talks to me in a way that sounds condescending and not too attractive for sure when I ask her something simple. I see that in her body language. At her worst, I feel she wants to push everything for me to do (and even tells me to do her favors every time) but I didn't and wont let that happen. It really sucks bc I got that huge feeling that she does not want to acknowledge my importance and appreciate my kindness, reliability, and thoughtfulness to her. No, this is not only one time of her extremist behavior. This has gotten to a point where I feel there is/will be a pattern of great days with her and then suddenly days I really wish I don't ociate with her. Her behavior is very changeable. I don't know if you would consider this person two-faced. Based on what I told you, how do I deal with this person? How should I confront her if necessary? Right now conversation has took a turn from great to poor because I don't feel like talking to her anymore or even working with her bc of her changeable personality. It's like all of sudden the interaction became so incompatible. (Btw, she is a Gemini). It's now giving me bad vibes when I have to interact with her at work. Does anyone know from experience why someone might act like that? Which side is really her true side? Many thanks for all your kind help. I look forward to hearing from your valuable insights so I can learn and become a better and even stronger person.