Snow-
Well, per one of my prior posts, the REAL issues weren't as much about us, as it was about the family situation overall, combined with her depression.
The biggest 'change' I had to make was to show her that I really WAS listening to her. She seemed to feel that I wasn't paying attention to what she was trying to tell me. So I put forth more effort in understanding her side of things, and showing her that I understood them. I also had to work harder on ensuring that her and I were on the same team when it came to dealing with our kids. Often it seemed to her like I was treating HER like a kid, or at least it was the kids and I against her.
Those were really the main changes I needed to make. To show her that WE were a team, and that it wasn't her against the world.
Don't take me wrong about the OM in our situation...he wanted her to be with him. And in truth, I think he made a mistake when he told her not to come. He'd been convincing her the whole time that he wasn't 'pulling' her to be with him. He always did the 'devil's advocate' role with her...because it WORKED. He knew that it was the best way to get what he wanted...but it backfired that last day on him. I think that he expected her to tell him that she was coming anyway, and that she was still going to get on that plane. But...she didn't take it the way he meant it, and that's why she ended up staying. God's hand was all over in this, IMHO.
I think that your NIL needs to very clearly communicate to his WW how much he loves her, how much he wants to work things out, and the changes he's willing to make to work things out between them. At the same time, he DOES need to set some clear boundaries and clear consequences if she doesn't follow them. She needs to recognize the CONSEQUENCES of her actions as well, and see what the positive alternatives are in working things out with her H.
Hope maybe this provides some fodder for you in this battle.