Over the years of being the Nightwatchman, Marian grew to notice the small things. Delicate sounds, the 'sense' of someone being there, all the small things that generally gave someone away that they didn't realize were there, were things she'd trained herself to pick up. It was the only way to stay one step ahead of the sheriff's men.
It was easy enough to notice when Matt showed. "What do you suppose he'd say? I don't think he and Hansel got on very well." She wasn't sure how many words Robin and Matt had. But she saw little harm in asking the young man.