I think anything you can do to comfort and feel safe as you begin to go into this stuff with T is a really really good thing. As in not just one thing, but as many things as you can think of. For me those safe things and internal places built up over time to include music, calming oils, soft lights, comforting blankets, special objects (from T and friends ,and selves), and self care like comforting foods etc.
Some Ts like to help clients build up self soothing / self care skills before delving into traumatic stuff, which I think is a very very good idea. Going through unprocessed trauma is intense and difficult work. It is REALLY hard work and at times it is emotionally overwhelming and , but it helps a lot to go into it armed with lots of self supports in place. The more the better. Use whatever you know calms and supports you. All of them. As often as possible!

The tapes that play over and over for you and keep you silent in T seem to be so inground that I think it will take a little more than your T realises to break them... as in, when you are in that 'bad space' I don't think you would yet have the ability to get yourself to a calm place without help from t. I like the idea of a signal... like lifting a hand or something, that indicates to T that you are trapped in that place and are unable to talk. It would be really awesome if you and your T could come up with strategies for her to help you find your way back when you are stuck in that place.