How much better it would be if your WW acknowledged your discomfort by making the decision not to go. A truly remorseful WS should never pass up the opportunity to prove to the BS that they matter.
I firmly believe that R means the WS must make the BS their #1 priority.
My WH has spent 2+yrs fixing the mess he created and proving to me that he could be a far better person, H, father because he wants to be. I feel very comfortable saying that my WH would not go to this function...he gets it.
Your WW does not appear to get it.
I would voice my objection to her and let her know that if she decides to go she should pack her belongings and take them with her...never to return.
ME: 54 BS
HIM: 61 WH
Married: 28 years
in R 3.5 years and it's working but he is putting 200% into it (as he should) to make it right again.
The truth hurts, but I have never seen it cause the pain that lies do.