It's hard to say without knowing temps, setup, etc. but I've seen this behavior in snakes with respitory infections. They're wiping the mucus from their mouths. If you see any drool or there is any evidence of drool on the glass, I would take her to the vet. If you're temps are ok and she's eating and seems otherwise healthy, it could be she's about to shed and is trying to start it although mine rub on logs and such, not the glass. Good luck with your new pet. They do have a tendency to grow on ya.