This is the point where me and Mandi switched rolls and I looked after the kids. For whatever reason she clashed with the daughter, someone said it was the attention daughter was getting from me and the 2 older boys???
Not saying that's what you should do but could be worth being careful around them both. These women have far more stuff going on internally especially after child birth.
By the way, mum and daughter are closer now than ever, need a bloody crow bar to separate them when together.