You need to calmly tell W that all discussions related to D will need to be handled through L and you will not be talking any more about it to W.
I think it is time to step back and let W handle the car stuff. Just state in a matter of fact way that W will need to learn how to handle those things herself as you two are getting a D. Politely turn down those requests for assistance unless it is about the children. Otherwise, W is just gonna have to learn these stuff sooner or later.
