Cora glances back and forth between them anxiously, because on the one hand, Derek actually wanting to spend time with her is something she's been wanting for a while. But at the same time, this was supposed to be her and Abigail's time together. It's really uncool to have your big brother crash your date.

So in that turmoil of not wanting Abigail to leave and being exasperated with Derek's timing, her response comes out as: "Now?!"