Usually that's a sign of overgrooming due to stress or depression. Have you been spending enough time with her? Did you change her feeding schedule? Her typical daily schedule? Did you change her diet? Is she the only glider you have? She might be feeling lonely...

If you see any sort of bite wounds or redness on the bald spot, please bring her to a vet -- there's one in Taman Megah, the vet's name is Dr Yeoh. He's seen a few gliders before this. If you leave the wound untreated and if it gets itchy or uncomfortable for her, she'll start to bite into it and this is a form of self mutilation. Gliders have been known to bite their tails off or self mutilate when they are in pain. This can be fatal if not properly looked into. I hope she'll be okay soon.