While I don't know if I can really tell you what to do, one thing my therapist said to me when we started is that if we did any work related to trauma she would first need to make sure I had coping skills and could handle it safely. It sounds like you are diving in headfirst into your traumas and are struggling without anything to fall back on as you said. So, I think that is at least important to tell your therapist what you are experiencing. As her first client she probably is a bit intimidated, but if you have a lot of severe trauma I would question if you would do better to work with someone that specializes in that.
If the bathing issue is related to trauma then I could see why working on trauma is important to fix that problem. However I wonder if there are other ways to work on it and reduce anxiety that don't involve delving into the trauma at this moment? Also have you seen an occupational or physical therapist? I wonder if they could help with the back and shower issues. Like if there are any other assistive devices that could help. I hope you can get the help you need.