I think this is a difficult time for her, and none of her reactions will seem 'normal' to you. If she is seeking help, and is given a diagnosis, she may also take this hard, but she will need support. And at least it offers the opportunity for her to seek help, including medical intervention.
Personally, I think she's going to need you more than ever. She may not show it, but if I were her, my world would fall apart if my fiance moved out just as everything is about to bubble over. She needs your support.
This must be terribly hard for you, and you are going to have to walk a fine line between helping her and making sure you are not selfless and do still look after yourself. The sooner she can get professional help, the easier it will be for things to slot back into place.

I am still confused as to how the bipolar idea only came about recently. If she has only recently started acting out of sorts, I'm assuming something must have triggered this. Otherwise, is there anything between you that happened and her actions are now not acceptable to you anymore?
I was dx'd 3 years after my bf and I got together, and it wasn't easy. Sure, it explained a good few of my actions, and helped my bf and myself understand my brain a bit better, but I still need to take responsibility for my moods, meds and therapy too. He will tread a little more lightly around me, but it ends up a give and take - a lot of understanding