John, I think if you push the point right now, W will walk. I don't think she is ready to deal with her guilt. I think she has to rationalize it in her own mind.
I think you should take your D aside and explain to her that when people are depressed, they sometimes make poor choices. Maybe you might want to use the word unhappy instead of depressed if you think it might get back to W. Anyway, I would explain to D that Mom is feeling really sad and needs her to be kind even if she is angry. Maybe you could suggest that it is okay to tell Mom that she is angry, but needs to be respectful.
We had a rule in our family that nobody used anybody else's things without asking. I don't recall anybody ever saying no (except maybe with the cars), but it was a courtesy issue. Never-the-less I think it is an issue with W because she feels ganged up on. In her mind she made a sacrifice.
I think if W gets her depression taken care of and you get some family and relationship things worked out, there will come a time when you might get an apology. I think it will take some time. I just wouldn't push for it right now.
I know it sucks! I certainly know why you feel entitled to have her say she's sorry.
