Thank you so much Xerox and Tickling . Really mean that 
I genuinely feel like walking out of the door this morning and not coming back for about five years. (Mature reaction I know!
). I definitely need to step back more but it's difficult to give DH the "bad cop" role because he simply isn't here enough, certainly not for day to day stuff. And he doesn't really "notice" mess or rudeness to a degree (because it's not directed at him). So it's a vicious cycle!
However, I know it's cycle, that being the adult here, I have to break. And I know it sounds pathetic (and a tad over-dramatic) but the more she "attacks" me verbally, the more beaten down I feel, the less able I feel I have the strength to break out ifyswim. I know I have to pull myself together and do it though!
On the positive side ...having been in this position before ...I'm beginning to realise it's a bit like the worst of childbirth, in that the onslaught comes, and then motherly love (or sheer fatigue!
) helps you forget the very worst of it ...until the next time. 
And gosh yes, I so recognise that scenario of every suggestion one makes (desperately trying to be helpful) being "stupid" "wrong" "ridiculous" ... (sigh).
Xerox your post has made me think. I genuinely don't know if DD believes what she is saying or not. Maybe she does in large part and just can't "see" that being asked to take five school shirts ( that have been washed and ironed for her no less!) upstairs to her wardrobe, is tantamount to three days down a salt mine
. She definitely does seem to hate me at times. Maybe they just need that level of revulsion to become adult and leave? Maybe I am a crap parent compared to others? (If I am honest, DH is much more naturally "maternal" than me in some ways.) Right now I am done with the analysing though and just want this "dark" period to be over.