Yeah, finding retic teeth in an enclosure is not an entirely uncommon scenario. She may have damaged it biting at the glass at some point, or when she was working on a large prey item. Could also just be a tooth being pushed out with a new tooth behind it. If it's not effecting her, don't worry it should come out on its own. If you start noticing abnormal behaviors, or swelling above her lip, start to worry as it could get stuck and form an abscess.