change is difficult, especially when you have been having issues with boundaries being placed, and trust fluctuating. I'm sorry she ended up messing the schedule so much. Do you think you can talk to her about it (maybe through your art?). Soemtimes just saying things helps me feel better, even if nothing changes (happened last week with T, then my thinking around things shifted, so it's better in a different way this week).
Also, if the hissy fit helps, go for it? (maybe at home if you are worried about social convention). Again, I use my art for stuff like that, or the journaling (though I am deciding she will not be seeing as much of the journaling anymore, it's messing with my ability to say things in session).