Hairy, Stay calm. Let her make an ass of herself. She is the one who has to live with the raving lunatic that she can sometimes be.
She knows that she is being ridiculous by talking to a 13 yo about their mother, as if the child doesn't have any loyalty to her. She intellectually knows all this--she is just frustrated and angry at the situation that she finds herself in. Someday when D3 is a teenager she will reflect back on how she treated her stepchildren and will be overcome with a deep sense of regret.
One thing I wanted to ask you: Does your W like children? She sure doesn't seem to have any empathy for your older ones and from the sounds of it, they could use it. I'm sure they are difficult to be around; what teen isn't. I'm pretty sure that everyone who came into contact with me from the age of 12-21 hated my guts. What else is new? Your kids didn't invent being an annoying smart-mouthed snot, after all.
I hope she calms down. Just keep steady and don't let her infect you with her crapola.
HP
P.S. I think reading glasses are extremely sexy. My mouth is watering just thinking of them.
