"Nel, I can get it--" Even with a cat on their lap, their little sister's condition is worrying enough that Feste wasn't really going to make her move. But... if she's got it, then they're just going to make sure she's wrapped securely in the blankets once she gets back.

Bells, sensing Feste's motives, will even move to sit on Nel to make sure she doesn't do that again. And so that the warmth of the cat might seep into her.