Some gliders sleep on their back so it could be normal. Just keep an eye on her.
One of my gliders would sleep deeply on their back with their legs in the air and I honestly thought they were dead. You could pick up their limbs and gently tug without a response and everything. But they'd wake up when I tried to pick them up.
I called my bf over and everything like " oh no I think so and so died" but nope. They've since grown out of sleeping like a dead person.