Good for you!! I'm not much of a spiritual person (raised die hard catholic.. catholic school etc), but I believe that it's definitely helpful. I've thought about going to church with the D's. They do need to learn about God. I feel a little guilty about not taking them.
You know what.. don't torture yourself over the long distance thing.. try not to think about it.. I know.. easier said than done. Did you confront her about keeping D up?
To me.. that would show a position of strength. It would tell her "I don't care what you do, but you better screw your head back on when it comes to our D"
Also.. what's your friend and family sitch? You need to surround yourself with people who will support you. It's a moral imperative.