Sounds like a recipe (no pun intended) for drama and unpleasantness.

Your ex-bestfriend had an affair with your husband, married him, and had the audacity to call you about how unhappy she is with him and expect comfort from you. Now this. She's not a healthy person. There's no way this will all go smoothly and stay professional.

You've been doing so well without these people in your life. As far as you know, they haven't changed. Why would you let them back in?

I can promote my business to those people.

And they'll think "Yikes, she must be down bad if she's actually doing this gig," because there's no way your identity and history isn't going to be gossip spreading like wildfire among the attendees.

I just avoid her as much as possible then it will be good.

How? She obviously doesn't care that you want her to leave you alone.

I'm late and you've already made your decision, which I'm guessing was to go ahead and do it. I hope you at least got advance payment.