It's just the silly game they play where they think they can send you thought waves of guilt and shame by their mere presence plus a dirty look in case you are in doubt about your status as something gross that needs to be scraped off the bottom of their shoe.
Just have a big smile and a loud "top of the mornin to ya Miss Sally. Nice weather we're havin. You have yourself a great day now. Gotta run, see you next time."
That will really piss her off or it will break the ice either way win win.