I agree with lcause and Chris, but I am not sure about one thing. Did she just bring this up out of the blue or did you have advance warning that there is a new teacher?
If she just sprung it on you and you couldn't go, you could say something like this to W - "could you please let me know in advance so that I can make sure I am there for D."
You guys need to communicate better when it comes to the kids, but that's about it. I had a kerfuffle about this last weekend and I realized that I need to be more proactive and communicate better with W about the kids - and that doesn't really go against DB/DR. Just don't find other ways to contact her or keep up communications.
