Mediator could help is he or she is honestly committed to being neutral and objective, but you won't know that in advance.

I had three mediators to help me in my situation with my unethical therapist and only one of them was helpful. The other two just added to the trauma by being clearly protective of my therapist and putting all the blame on me. So, while you can keep mediation in mind, make sure that the mediating therapist is comfortable with the task and wouldn't add to your trauma.

I'd suggest though to clarify for yourself what you want. If you want to come to a mutual understanding and reconciliation with your therapist then don't contemplate any punitive actions against her until you realize that reconciliation is not possible. The agenda of reconciliation and the agenda of punishment are mutually exclusive and no action will be successful if you try to execute both.

I have an impression that there is a internal rift within you about what you actually want, and whenever such conflict is present it's better not to take any action until you sort it all out and get clear with yourself about what you want. Honesty is paramount when you try to answer this question for yourself.