I had an elderly glider, Nand, who lost an eye and while initially accepted back by his colony, after complications, he was ultimately ejected. He lived for over a year that way and had multiple cysts during that time on the scent gland on his chest. He was at the vet
a lot. He was a happy boy in spite of all that. He, too, switched to being awake a lot during the day. I suspect this may be common with only gliders as it is a way to see their people. My healthy gliders will also wake up at strange times if I'm not available when they're used to, just so they can see me.
like your girl is healthy and happy if she eats and plays. Unless there is something else medically wrong (check!), the recent change means she could very well be depressed from being lonely. Hand-feed her. Give her a lot of love, let her sit in your lap when you can or take her out with you when it's reasonable; make sure she spends as much time with you as you can to elevate her mood. If you go out of town, have your petsitter hold up the phone for your glider and talk to her. I did it for Nand and later the rest of my colony, and he would grab the phone and hug it tight. I would tell him that I loved him, was proud of him, would never ever abandon or reject him, and that I would always come home for him. I would excuse myself from business conference functions to "go call my glider". It worked. It helped him keep going when I wasn't there with him.
Nand lived as long as he did because he was happy enough just having me. You can never fully replace a sugar glider companion, but you can develop a close and loving relationship that will make your glider fight to live. You're not making something from nothing. You are living out an atypical situation with an atypical glider, but that doesn't mean she's less, it just means your relationship with her will be more. I used to say that since Nand only had one eye, I'd just love him twice as much.
Good luck. It sounds
like you've done a lot for this little girl. I hope it works out and she lives a fulfilling life with you.