Have you thought about having her go to counseling? That could help her deal with this.
Maybe you could just tell him and ask him what he thinks about sending her to counseling. Think about HOW you say it. If you say "D has been destructive ever since YOU moved out", then he may take it as you guilting him. You could say "I am worried about the affect that OUR separation is having on D, she has been very destructive lately. I just wanted to get your opinion on havng her talk to a counselor." Maybe he would be more receptive if you offer a possible solution to the problem that doesn't involve him coming home.
I don't know, just throwing ideas out there. Maybe you can start a thread in the separated forum and more people can help you with this situation.
