if you keep one on too long, depending on how new it is (do we know when it was last fitted???) you can get blisters and decubitus ulcers from keeping it on or walking on it too long. Sleeping in one... have not heard of that, as a professional nurse, at all. Anyone else with a prosthetic who sleeps in it feel free to chime in. It is kind of like sleeping with your dentures in.
What also is important to keep in mind is that with children with prosthetics thy must CONSTANTLY be refitted as they grow. At her age she could go thru a good dozen or more to adulthood as her long bones grow. I personally wonder if her prosthetic/amputation was being actively followed by a doctor once she came to the US...
And trust me.. if this SM was making her walk around on a prosthetic that was too small for her it would have been beyond excruciating! (and until I see some documentation/media reports that she was being cared for state side I just don't believe it was happeneing. not at all... and my HEART HURTS ALL THAT MUCH MORE! AS A FELLOW CHILDHOOD CANCER SURVIVOR)