Ava was so busy disagreeing with Viola's sudden interest in The Horrid Mr. Fox that she had not yet put together two and two. Not until it was repeated just how 'good' she'd been with him (that was patently untrue), and, well, having Viola specifically say that Ava would be looking after him. That's when she realized how terribly the situation had gotten away from her.
"Wuh!" Her aborted attempt at arguing turned into pursed lips and a face redder than before. She was acting like a spoiled child! And it was entirely Mr. Fox's fault. And Dr. Cress's, she supposed.
"I can manage, ma'am," she said, trying hard to stop sounding utterly opposed to the idea and failing.