I want to send you commiseration too--it all sounds VERY familiar, and yes, I too am thinking "If she is this hard at 8...." quite often. My DD is also incredibly relentless, has an astounding memory for things I said once 5 years ago when I was half-asleep, and can beat almost anyone at their own game. She used to explode a lot, but recently she's moving towards "Fine, whatever" with no show of emotion at all--and she will not fold.

I am working towards reaching her and trying to acknowledge her pain and anger rather than disciplining more.