Female co-worker cycles between hot and cold

I have a new co-worker since a couple of months. When I met her my long term relationship had been slowly dying for months, maybe longer. She was assigned to work with me one day a week and we're in similar fields. It seemed we hit it off immediately, as friends I think, I soon started liking her a bit (nothing too serious though). She briefly mentioned something about her boyfriend once or twice a week (when it was relevant to the conversation) and I mentioned my girlfriend. Then as time went on we started to have deeper conversations, teasing, joking, etc... but we were still not seeing each other outside of work. I really liked her intelligence and conversation skills. At one point she made a comment about her boyfriend that I didn't go into but I suspected meant she wasn't feeling like she had enough in common with him (just like I felt about my girlfriend). I then went on vacation and decided to break it off with my girlfriend soon.

When I got back from vacation my co-worker was ice and ice cold towards me (verbally and in terms of body language: crossed arms, shoulder turned away from me, etc...) and since I had started liking her quit a bit by now and was already feeling pretty badly because of the decision I had made I basically crumbled and spend the rest of the workweek being nervous and quiet. My co-worker also became very nervous and quiet around me. That weekend I broke up with my girlfriend and the next week I told my co-worker about it when we were assigned to work together in the same office room. She immediately told me she was having similar troubles with her boyfriend (and in later conversations it really sounded similar to my own experience) and we spent the day like we were completely comfortable around each other again. Then the next day her nervousness and negative body language were back, she really seemed to be avoiding me.

Since then it's gone back and forth like this for a couple of weeks: she'll open up and tell me very personal things (quite often things we have in common) when for some reason I can get her alone and talk for a while, but she does have boundaries and I'm certainly not running around doing favors for her or begging for her attention so I know I'm not friendzoned. I now know she's been with her boyfriend since she was a teenager and so has zero experience with adult courtship rituals, this has given me some more confidence so I don't reflect her nervousness as much as I used to, but it still seems like a power struggle at times, depending on who's sitting/standing, who walked up to who and who's in a more confident mood. She's usually pretty outgoing but I know she has a nerdy/dorky side to her (I'm the same) that she doesn't like showing in public, or really to anyone at work. I know girls with a similar level of physical attractiveness to her have liked me in the past and I know from an old facebook picture her boyfriend looks a bit like me, so at least it's not like she's way above my league in that regard.

To give a typical example of this cycle:

The bad: The day before yesterday I went for lunch with a group of co-workers, she happened to go at the same time. We all took the same elevator and when I stepped in her whole face turned red and she literally stepped to the side to hide away from me behind another co-worker's back. She then treated everyone at the table as if they were the most interesting people in the world though I saw her quickly glance at me twice from the corner of my eye. She ignored me for the rest of the day except at the end of the afternoon she came by my office and talked about something work related. All the while very anxious, touching her throat, shifting from one foot to the other.

The good: early yesterday morning we had to go get another co-worker from another floor together. This meant 1-on-1 contact that she couldn't avoid and she repeatedly asked me questions even though I was giving short answers because I was a bit mad at her for het antics the day before. But then I engaged her and she seemed friendly and a bit less nervous, even joking a bit. When I walked past her office afterwards I saw her secretly glance at me (only her eyes moved), but I was glancing myself from the corner of my eye and I'm pretty sure she noticed. At lunch we actually talked for a few moments and she didn't seem to avoid me anymore. Then in the afternoon we had a meeting with on (much older and definitely not her type) co-worker and she actually dared to sit next to me, was friendly, warm, had her legs faced to me under the table even while talking to our co-worker, she played with her necklace. Then we had more conversation on the way back and she hesitated when we walked past my office. We struck up a conversation with another co-worker in my office (also much, much older and definitely not her type) and this went on for half an hour during which her and I cracked a lot of jokes, teased each other, smiled at each other, stood close to each other, etc...

I have two competing theories slugging it out in my head:

1) For some reason she just doesn't like me "like that", but she knows I like her and wants me to back off, on the good days and/or when I talk to her for a while she thinks I'm over her and she'll open up because she does like me as a person. The occasional glance from her is her checking to see if "that guy who just doesn't get the hint" is still looking at her.

2) She does like me "like that" but is very awkward since she's basically still a teenager when it comes to courtship and she is feeling guilty/confused because she still cares for her boyfriend in some way. When I talk to her for a while 1-on-1 I get her out of her shell. The occasional glance from her betrays her interest.

I need answers/insights/closure, at the very least so I can defuse the tension or know how to handle this sort of thing if I meet someone else like this.