Duck might be nesting

Hello ... When I was out there today, a female mallard duck came charging out at me from the weedy area under the classroom windows, along the north wall, just to the east of where the after-school kids have their plot. She then stood and watched me closely the whole time I was there. I wonder if she has a nest in the weeds, or at least is scoping the place out. Has anyone else seen her? I marked the location with a note. Maybe if we don't scare her too badly, we'll get to see some ducklings!