Welcome, I'm so glad you are seeking correct help for this poor glider.
A vet check is crucial at this point to really assess her state of health. It sounds like she's been malnourished and most likely kept in cruddy conditions to be in the state described. It's so sad, but the good news is, is all ready to improve in your care. Hopefully she will not require meds, but it's definitely important to rule that out.
A proper diet is key in getting her back to health. There are several recognized diets around that have been successfully used, keeping gliders in optimal healthy conditions. I recommend going through the list and finding one that you feel will work best for your budget and lifestyle as far as gathering the proper ingredients, preparing, and serving the diet plan as directed.
I'm going to link you to Candy's website because she offers links to some popular diet plans as well as her own diet plans, giving you a good bunch of options.
GliderKids Feeding Plan
I also recommend reading through her sight, as she gives extensive, researched, information and puts in a easy explanatory form.