Funny, that's exactly what the MC said to me. "Why do you engage?" Just say that you won't argue with her, and walk away.
Point taken.
And funny you should mention "whipping boy." It's exactly the term I used when I told her to lighten up last night.
And finally, as a co-worker just mentioned to me, this is not about "taking back my power." Putting this all in terms of "power" or "control" is buying into her framework of the relationship. No, this is about two adults, with equal rights and responsibilities, treating each other with respect and love.