Oh cakes, the OW is not the problem. As WWIFN says, the problem is your husband. If your husband was fully supporting you at these events, you would not mind that she was there - you would just be strong together. The person who betrayed you is HIM, not her.
I know it's easier to blame an outsider, but I think that if your relationship was strong enough you would not feel threatened by her.
Forget her and concentrate on him, seriously. If he is not doing enough to make you feel loved that is not her fault.
I can see why you do it, but you shouldn't be emailing her. She is not the person who committed to you. You need your husband to be backing you up here - she is probably a silly cow - but nevertheless, you shouldn't need to contact her and ask her to respect your relationship - it is your husband who needs to do that.
He thinks you are doing it to hurt him? Is he mad? He sounds very selfish and self absorbed. Please take a step back and see that the OW is not the problem here.
It sounds like your H has not committed to you and the recovery process - until he does, you are simply misdirecting your anger at her.