There is no explaination. No rational one. In their world, where the world revolves around them and what they want, they are blissfully unaware of the hurt and pain they cause those around them. Nice bubble if you can live in it.
Do this. If your D wants to talk to you about it, then try to be as unbiased as you can be in the conversation. If she doesn't want, respect her wishes. She is getting to the age that she is going to have to make decisions regarding her relationship with her Father and grandparents.
I'm very sorry for the hurt he has caused you and your D. It will be one more of those things he will have to wrestle with on some dark night of the soul.
