When my mum had hospital stays when she was still in her own home, her accommodation was assessed by Occupational Therapists to check she was safe. She had to demonstrate that she could get herself in and out of her chair and bed, use the toilet safely and make herself at least a drink - they didn't take her word for it - she had to show them she could do it.
Make sure the hospital know to let you know when any assessment is to be done, so you can be there. OT's are very good at spotting when older people say they can do more than they can, and will listen to what you tell them too. It's a necessary step to make sure your Mum gets what she needs, but be warned it can be hard to watch, especially if having to show someone else what she is capable of makes your Mum realise what she can't do ....
Thinking of you xxx