Narcissa was quiet, forgoing her chance to snap some unpleasant retort back at him about the state of things, just to rub it in his face of the mess he'd made for them all. It occurred to her then that she'd said far too much while in her anger-filled state. This was precisely why Narcissa did not get angry and instead opted to ice over. Doing the latter kept her from saying more than she intended, but when she was angry her emotions tended to get the better of her.
Her expression turned from anger to a bit surprised. She didn't want to lie to him, but how cold she say what she'd done? It was for his own safety that she thought she couldn't. "I'm.. afraid I fear the consequences you would face if you were to know." She turned away from him again to face the wall of books, as if perhaps she could disappear into one of their stories rather than facing the reality of the situation.