I want to show her that I am pulling away from her.
So I put myself in your wife's shoes and imagined what would rattle my cage. Here it is: "W, thanks for the invite. Can't though. I have something planned afterward, but I'm glad your parents will be able to spend that time with y'all."
Rattle. Her. Cage.
You don't have to say what you have planned, and if she asks, say, "Dinner plans." Then rush right out and make some