Is my fianc� bipolar?

My fianc� and I have been together for 8 years and have a 6 year old daughter. I believe my fianc� has bipolar disorder or something similar. Our relationship has highs and lows. We would be a perfect couple for months at a time and then all of a sudden she would freak out and want a break. She says she's not ready for a relationship and she can't take the pressure of me and a relationship. This has happened multiple times probably 9 or 10 times so far. When we are happy all she wants to do is be with me and repeats that she loves me and is so happy that were together, but when she's not she just wants to ignore me completely and do "her own thing". This change will happen rapidly in the matter of a day or two sometimes overnight. Here are some major things that have happened. She told me that if we didn't get engaged then she was going to leave me. So we got engaged and she was so happy, 6 months later she wanted a break. She wanted to get married and had planned the whole wedding our next step was to reserve the place and pay. All of a sudden she didn't want to get married. She wanted to move out and get a house so she searched and searched and found places, then we went to get approved. About a week later she changed her mind. A month later she wants an apartment so we found one, paid for it, signed for it, and all of our family along with ourselves bought all sorts of things for our new place. All of a sudden she wants to call it all off, cancel the apartment, return everything we bought, and she wants to break up now. Some background on her: she is constantly sleeping, buying clothes and accessories, and along with her lows she hates her job and wants to quit. It seems like her mood, interests, and thoughts does a complete 180 that lasts for weeks to a month at a time. The majority of the time she is the greatest person I could ever ask for. I am here for her no matter what and I want to help her through this. Should I have a talk with her about bipolar? Thanks