Why did my sugar glider die?

Why would my sugar glider just die? I have had her two years and she seemed perfectly healthy. I fed her the food for sugar gliders made up of dried worms and apples occasionally. she was barking and running on her wheel this morning and when I got home she was curled up like she was asleep ( but outside and not in her pouch) but she was dead. I am so sad about this. Is it because she was alone? I got her when she was already around 9 mths old from a pet shop and she would bite me so hard she would draw blood every time i picked her up. so i stopped picking her up but she would let me pet her in her cage and she would lick my fingers when i fed her. I just dont get it- i only had her 2 years.