I understand your concern about your baby girl. Like you, I have a single, female glider. Since many people agree that sugar gliders do better with at least one companion, I've been keeping a close eye on her for depression, changes in appetite and/or behavior, over grooming, self mutilation, etc. that can sometimes occur with single gliders. I've seen my little one walking in circles at the top of the cage. Repetitive motions like this can be a sign of depression or boredom (although she only does this in her travel cage, never in her larger cage where she has more room to run around). Occasionally I find my little girl asleep on the bottom of her cage and moody as well. Even though it may mean nothing, it makes me nervous so I've taken her to the vet. One time everything checked out perfectly. Another time they suspected parasites. Scary sounding, I know. But after a course of antibiotics she is now doing great. A wellness exam by an exotic vet is always a good idea to make sure our little babies are healthy and doing well.
Although gliders are nocturnal, it's not uncommon for them to be awake in the middle of the afternoon, or asleep in the middle of the night. Their schedules can vary, for many reasons. Like TaLuEl mentioned, she many be thirsty, hungry, or needing a 'bathroom' break. Or she may be restless and need to stretch her legs, so to speak. Do you have an exercise wheel for her? Toys for entertainment and stimulation?
With single gliders, it's important that you spend extra time with them. In addition to giving my girl lots of attention at home, I try to bring her with me whenever I go out (in a safe, zippered bonding pouch). She's been to restaurants, movies, and even the dentist.
I would continue doing what you're doing, keeping an eye on her and being vigilant. Make sure she's eating, drinking (you can check for dehydration by doing the tent test), pooping, and peeing. Have you had her very long? If not, she may just need time to adjust and get used to her surroundings. Enjoy your sweet baby girl!