Since you do not know what caused the male's death, it is important that you have the female checked by a glider experienced vet to make sure she is healthy. Fecal testing for parasites should also be done to make sure that is not an issue.
Have you already introduced the new joey to Sky? If so that could be a reason for the change in her behavior. It is never a good idea to bring home a new glider and immediately put it in the cage with another glider with out gradually introducing them both to the other glider's scent and doing careful introductions.
Your new joey should also have a well check up with a vet. If the two gliders are already sharing a cage or have had direct contact with each other - if either has parasites, you will need to medicate both gliders.
If the two gliders are not already in the same cage, the presence of another glider in your home could still be contributing to Sky's change in attitude. She may be biting you because she smells the other glider's scent on your hands.