So you have anxiety from your past relationship, from the cheating, this is totally normal.

And now your fiancée is triggering this anxiety, which she did not create, via a rather normal pre-wedding ritual.

Your anxiety is your problem, not hers. You can’t reasonably expect her or anyone else to not trigger you. You need to work on your own shit and heal to the point you can be in a healthy relationship without your PTSD ruining it.

This bachelorette party is just the beginning of your troubles if you fail to get treatment. You will continue projecting your past relationship onto your new one and your fear may become a self-fulfilling prophecy. Please get yourself to therapy, it will help!