If that is what happened with om coming in to town for the weekend, that would certainly explain the anger and attitude. Maybe she has suppressed her feelings of guilt, and the phone calls, calling her attention back to the fact that she has a H and children, brought them back to the surface.
Just call to speak to the kids, or to her about the kids, but keep your conversations with her short and sweet. And maybe for awhile keep a bit dark with her, and not be available to speak for hours on the phone when she decides to call you. I think you are doing well, and that you handled the whole situation as best you could, and she has no reason for complaint, except for her parents have called her out on it, and she blames you for that, too.
I think your staying calm and handling the matter was a great positive.
