I don't know about dissociation and processing trauma. One time when I caught myself and stopped my t talking about whatever and told her that it was happening, she tried to normalize my experience. She didn't even want to label it dissociation and talked about the different levels we might separate or disconnect in order to feel safe. I agree with her that a certain layer or type of dissociation can be and is useful in given situations. Maybe your t isn't aware of where or what extent you are dissociating or perhaps she feels that it is at a level where it can be a useful tool in your processing?

This is just a guess so take it as just me throwing ideas at the waterfalls and seeing if anything make sense to you... do you find that with repeated exposure to topics where you dissociate, you to become less sensitive to the exposures and are able to "last longer" before dissociating?