No offense but...
(sorry-I just couldn't resist writing that-input a little humor).
Go the party, be on your best behavior. Don't be vindictive, don't be a bitch. Just enjoy your time, leave space for her to enjoy hers.
I did walk out of our local poly community after someone my husband dated made a point of attending EVERY event I PLANNED. Including trying to attend events IN MY HOME.
THAT was rude. It is a small community-but as I didn't attend events I wasn't personally planning-and there are many who plan there own-there was no reason she needed to attend the events I planned. That was vindictive on her part-attempting to make it so that I had no ability to partiicpate without her in my face.
So be wary of your choices and your decisions. There is a fine line between sharing the group of joint friends-and making it impossible for someone else to enjoy the shared friends without you being in the middle of it like a possessive spouse.
"Love As Thou Wilt"