She doesn't know what to make of the change in his expression or how he seems to stammer, but not out of trying to analyze. It's that no one even taught her the social vocabulary for it; her best guess is that he got a sudden bout of indigestion. But her brow still furrows while thinking over his question. It takes probably a beat or two longer than normal conversation for her to answer.

" ... I'll stay as long as I need to- as long as I'm needed."

A slip, or could it be construed as clarification? She doesn't let herself dwell on that too long.

"Who are you? The town watch?"