It sounds like it wasn't 9 out of 10 for her. I do not intend to downplay what she has done, she is absolutely in the wrong here, and also considering what I will write next, it is her responsibility, not yours, to ensure she is herself. Perhaps she felt appropriated. Perhaps doing all those things together meant that she lost any notion of who she was without you, that all that she was and did was determined by who you are and what you want.
Again, it is of course not possible for you to notice that (if that's what the issue is), as she clearly didn't communicate it. It is her responsibility and her actions thereafter (i.e. leaving you and setting an ultimatum) place her clearly in the wrong. That being said, I've felt like doing what she did before (I never did just up and leave, but I have wanted to plenty of times).

ETA: If that is correct, you driving her to therapy may also be unbearable to her, as it is her that needs therapy and it is supposed to be her thing, not yours, too. May I suggest instead of driving her, could you help enable her to drive herself?