Oh my goodness,how i feel your pain. I was in a similar situation of running into the OW this weekend. She, however, strategically planned it so i would run into her. UGH.
Your feelings are not crazy. The thought of any BS having to act sociable around an AP is physically sickening. I too, went into panic mode and was hysterical.
I think it is OK to have your FWH check and see if she will be there. He isn't breaking NC and contacting HER, he is checking a list. I think he is supporting you by helping you prepare for a possible encounter that may not be unavoidable. Advance warning is the best warning....far better than being blindsided and showing up and seeing her.
i see the OW on a regular basis, she lives right by me. If you can avoid the situation, awesome. Best thing you can do if you DO have to be in her presence is to hold your head high. Be strong. Dont let her make you crazy. Hold your WH hand, present a unified front. Dont give her the the time of day. Put on a brave face and let her know she didnt break you. While you may be falling apart on the inside, walk tall.
One of my favorite quotes that has given me strength thru all this is "Promise me you'll always remember You're braver than you believe, stronger than you seem and smarter than you think"
You can do this. We are here for you. hugs to you.