Gail, I just happeend to see your post. I too am wondering why it would bother you after 22 years because that seems like a long time, but for whatever reason, it bothers you and probably one of you will have to compromise... either your husband by not inviting her or you by allowing her to come.
Just a brief personal experience...my parents divorced about 25 yrs. ago and my dad has been remarried for about 18 yrs. maybe. My parents had a pretty bitter divorce in which they couldn't stand each other. My mom still doesn't like certain things about my dad, but they are able to be civil with each other and be around each other, which has been good for my sis and I. Alot of it has to do with my stepmom though. She has always been nice to my mom and will invite her always to join when there is a family get-together thing.
We have had many times when its been dad, stepmom, mom, sis, and me, and then maybe our boyfriends or friends (and at one time, my husband and now my sis' husband). Even last Christmas, my sister and I "hosted" and we were all together. We had an Easter, after I got married, where we were all together.
So... sometimes we laugh that it's kinda wierd but it's nice to have my mom involved rather than her being alone. I think though that also, now, all these years later, my father regrets divorcing my mom.
But anyways... like I said, alot of this has to do with my stepmom because she's always been very kind to my mom. But my mom has also been kind to her. She doesn't invite her to things, etc. but she's always been nice to her and civil.
I don't know if any of that helps you at all. You might be in a totally different situation with a bitter ex-wife.
Maybe if you can view it as just one day? And see it as a denial of yourself/sacrifice for your stepdaughter.
It will be up to you and your husband obviously.