As you have probably guessed, I can go on and on sometimes. Will try to keep this one short. I may have left you thinking you should totally discount W's comments or concerns.
I hope you have come across some threads on using the phrase "I'm sorry you feel that way." It validates that you heard her. It does not say you agree or disagree. It says you have some compassion for her concerns. It opens the door for you to share any comments you have, if you wish to. It might disarm her slightly if you want to start a discussion.
There may be times when you want to then thank her for pointing out something that she thought would have been obvious to others, but that you had not considered it that way. You may see opportunities to acknowledge her criticism as constructive and worth approaching with a an open mind.
And of course, there may be times when you follow that line by gently pointing out that she seems unnecessarily critical in this particular matter, as if something else may be bothering her. Instead of just saying she is wrong or that you don't agree, leave the door open to the fact that something is obviously troubling her. Be the rock of stable communication. Perhaps there is something else she would like to talk about. Maybe world peace. Perhaps the economy, or that her first son could soon be in harm's way.
These may or may not be DB, but they are just handy dandy ways of dealing with other people. We all need to do a better job of that. Does it matter if she changes her whole attitude or behavior as long as you are being the best person you can be? And if it does take the edge off of being in the house with her, then who knows. Low expectations makes the baby steps more rewarding.