This needs to be her issue, not yours. As you said, she is considering professional help to understand her anger, and this is probably the best course of action. At some later time counseling as a couple might be helpful so you can understand her issues too.
You should stop trying to analyze this on behalf of the both of you. There are too many possible issues on her side. Many of them might predate your relationship, so there would be no way for you to try to analyze them or work on any solution.
Possibly she perceives some situations between you as threatening her security or status quo (comfort zone), for whatever reason that might have nothing to do with you. This could manifest itself in various kinds of irrational response, including anger.
But still, she needs to understand the causes of her anger and find the resolve to move forward.
One concern with questions like yours is that we only hear one side of the story. Her side is just as important.
If she were to write a question like yours about this topic (the anger) from her point of view, what do you think it would say? That question would be just as important as yours.
Finally, there is a term that is commonly used in describing relationship issues, co-dependent, that you should be familiar with if you aren't already. Basically, any behavior you tolerate you by default condone.