I am a little apalled that she can't handle your mood in a therapeutic manner. Ending the session isn't therapeutic. If you're not in a place to do trauma work, much else can be done. If you're not in a place to be calm and serious, there are plenty of ways to still connect and benefit from her time.... if she herself is in the right state of mind. I think the problem is hers, not yours based on what you've shared so far.

If my therapist thought to end sessions because I wasn't communicating in some window of tolerance.... she wouldn't be my therapist. Therapy for me is having someone be there for ME, whichever part shows up, however I'm able to express myself.

I would feel very invalidated to have a session cut short like that.