Ohhhhhhhhhhhhhh, what you've said re differences between the children is ringing SO many bells with me, Harpsi!
I deal with it by going to work four days a week, so I can be calm, placid, doesn't mind being mauled Mummy on the three days I'm with the boys. I appreciate that's not likely to be an option you'll consider though
I find it easier to deal with Fridays (DS1 goes to preschool in the morning, I take DS2 out somewhere while he's there, bring them home, we all have lunch, then we all sleep in the afternoon.
So I would try, if at all possible, to steer DD2 round to being an afternoon napper.
But I remember this being the transition time from two naps to one for DS1 (DS2 dropped his second nap when he was about 6mo [grr]) so it's a difficult age from that POV.
Email me if you want to, lovely Harpsi.
Oh, and it's just a phase and she'll grow out of it. And she will. But maybe not tomorrow...