She shakes her head again, though this time, it's less at him and more at herself: some last vestige of her sensibility insisting that this is a bad idea, while the rest of her gets caught up in the thought of actually going to such an event. Not just imagining it, but being there.

Things are different here, aren't they? She's still working class, but so are most people. Coming to Darrow tends to be something of an economic equalizer. And if she can't quite shake her own class-related insecurities, she's not oblivious; she knows most other people don't share them. Look at Biffy: he's every bit as well-mannered (and well-dressed) as Thomas, but he's never been anything but kind to her, and she's never really considered herself unworthy of his friendship.

He could probably help find her something to wear, now that she thinks about it.

"No," she says in resigned response to Thomas's insistence that she could think about it. She could pretend to think about it, but all she'd really be doing is fretting over the decision she's already made. Belatedly realizing he might take that 'no' as a general rejection, she bolts upright in her chair. "I mean--not 'no,' that I don't want to go at all, I... I would. Very much."