Fiona doesn't know Snape well enough to tell one bad mood from his normal grinch-like demeanor; she assumes this is just another day at the rodeo. She sets her supplies aside, kneeling down to start organizing the larger chunks of saveable matter, like Snape has. He's clearly in charge of books, so she'll get the loose papers scattered about, and mark off the occasional pile of broken glass.

She hasn't yet decided how she wants to deal with his sniping. Is he the kind of guy who will fire her if she talks back, or will he respect her more? Best play it safe for now. "Yeah, had to grab some supplies," she indicates them with a dip of her head. "What rooms got the worst of it? I'm guessing we don't have a cleaning staff yet..."

As for the tight ball of emotions in her chest-- the anger, the frustration, the terror at now knowing what death feels like-- well, she's been bottling emotions up and hiding them under the rough rug of work since she was fourteen. It's no longer a conscious process.