I think the most chilling thing is that from her point of view I don't think she even realizes what she did was wrong.
I have too much hate built up. Anger is healthy, it protects you from future harm and pushes you forward, but this hate is seething and rots me from the inside. I know I need to let go of the hate and move on, and most of the time I'm ok, but then seeing her just triggers the rage and my brain starts to shut down under that cry for vengeance. It's not healthy, but I'm stuck. There was so much psychological damage done before and during the breakup/cheating that I haven't fully pulled myself together from that yet even after these past couple years, and seeing her triggers regression. It's like trying to heal a scab that gets ripped open every time I see her. Maybe it's all just scar tissue now.
I actually am considering freezing the event if she starts appearing regularly. "My apologies, the weekly dance is now cancelled. Certain personas have made the environment poisonous for me and I can no longer operate under those conditions."
That in turn will be even more damaging. You may want to look into getting someone else involved who can take over the organization if she decides to show.