And is now living with BM, I imagine it's teen drama, and things will change when she calms down, because honestly, I'm sure BM's home isn't easystreet either. I also suspect to a certain degree that DH is being manipulated, not necessarily for malicious purposes, but because that's just how SD deals with life, instead of direct, honest communication. Once she gets what she really wants out of him, it will be like it never happened.
Anyway, YDS was the instigator saying true but also very unkind things, which pissed her off. To me, this is just what happens when you give one child special treatment over the others IMO. I think the big thing is that they do chores while she watches TV. In fact they have higher standards of behavior all around. She has said much crueler, dishonest things and gotten away scott free, so I do see the double standard, and it makes me angry that it's not acknowledged by either DH or SD. However, it did not need to come out of his mouth, and I don't want him to become a rotten person, so he was disciplined.
So now DH is in a huge depression because he's enmeshed not able to separate her teenage girl emotions from his own. Maybe also upset because he always prided himself on being the "best" parent, and he is blaming himself, he knows he gave her special treatment, leading to the argument. He didn't discipline her when she was mean to me, never made her apologize, which made me step down and out, further widening the gap. So at least this time our son and I are not the scapegoats, for the most part. He briefly tried to put some blame on me, but I shut that down quick. And really, she wasn't going to have an easy time getting along with me anyway, since BM is a jealous lunatic, and the apple truly didn't fall far from the tree.
So here's hoping this conflict brings about better and changed behavior all around. Maybe, finally counseling, which I have been begging DH for over a decade now, who knows? I'm just trying to stay strong, and not get involved, this is his kid, and his problem, he needs to be the one to resolve it.