my thoughts.
A good diet will have the needed vitamins in it, or the vitamins will be mixed in. the sprinkle on top method is very inaccurate. And does the glider eat it or eat around it?
I feed Ohpw with veggies and fruits, no vitamins added.
Give your glider attention, don't worry about a cage mate so soon, take time to learn your glider and for him/her to bond with you.
a vet visit sounds great. ask lots of questions.
Our gliders did not eat the fruits and veggies when first switched their diets. some of them took weeks/MONTHS to start eating it. they still don't eat many fruits. but peas, green beans, corn are all eaten most nights.