As you know, boundary setting in the most simplest forms is this:
"If you do this, then this happens."
When your W is vengeful, spiteful, and plain disrespectful, you can say to her: "W, I will not be spoken to in this/that manner. When you are calm/calmer, then we can speak. I am removing myself from this behavior."
Then stick with it over, over, AND OVER. Until W gets it and changes her behavior accordingly. You do need to stand up to her.
