Thanks for sharing this. From my perspective, there's a rather wide gap between what the experts tell us we
should do & what we can often manage to come up with in the heat of the moment, so to speak. Plus... from what you wrote it sounds as though you're still pretty new to all of this. So I would say, don't beat yourself up too badly over your work with this one particular girl. It sounds as though she is difficult under the best of circumstances... & you're still learning.
Now, having written that... it is true, I believe, that what we would most like to do is not always something we're temperamentally suited for. So I think you're right to consider if how you're reacting to the children in general is appropriate, or if you just seem to be "going off the rails" more than you're handling things correctly.
If you find yourself repeatedly reacting inappropriately, & you don't seem to be able to figure out how to improve, then perhaps there may come a point where you have to confront the possibility you may just not be suited to doing the type of work you're doing. There's no shame in that. We all have things we're good at... & things we're not. The only shame would be if you denied that you were reacting inappropriately over-&-over & you did nothing about it. I think it's great you'll be seeing a new therapist next week. Therapy should be a good place for you to work through this. To my way of thinking, the fact that you're sensitive to these issues is a wonderfully positive sign.
P.S. Hope you keep posting!