Some other thoughts from me:
I know your neighbour didn't have time to organise stuff before her accident, but 2 weeks is plenty of time to make alternative arrangements.
Re-reading the OP, I see a couple of things now, the ward sister says "she's fine", that is from phone calls which you are making to the ward?
Just to clarify, it may be a possibility that despite her giving your details the staff may not actually have permission to speak to you about her condition at all. They aren't denying she is there, because you already know otherwise so that would be pointless and so when asked how NDN is "she is fine" basically says something and nothing. Has answered the question but still not actually told you anything.
Im in hospital regularly and one phone call sorts out the cats feeding times etc and how to access the house as well as packing up a bag for me and what I need in it.
One the one occasion, the cat was outside longer than intended (about 4 hours without being checked on and it had started raining) and couldn't get back in, she went to my next door neighbour and lay in her hallway underneath the radiator, until some1 shouted for her and she came home to play, eat and go to sleep.
As a pet owner, she needs to have a plan in place for the pet in this event.
They may try to discharge her, when she is discharged from the hospital it will be a lot harder for SS to arrange even temporary help while she heals.
As they will have discharged her on paper at least to neighbour (who may not necessarily know about it - you) and then the fight for other help starts by which time any possible help is in sight, she is long healed by then. In the meantime, as she sinks at home without the use of arms/wrist, you are the point of contact listed by her on notes by now as they contacted you to organise delivery of the commode.
While she is there effectively blocking a bed pending being medically fit they will actively be trying to "offload" onto someone else/ anyone ie you. She may think it will "just being neighbourly", it's not at all. That is way over and above.
Has anyone else been in the house that you are aware of? How is she getting her washing/ clean clothes etc? If she has a supply of these there is probably someone else visiting her and you are left looking after the cat and its health problems with care needs. You could have acquired a cat by stealth even if you don't want one.
As you have the keys to her house at this point, I would go and take a lot of photographs around the place with a timestamp on them if possible, as you don't know her well at all so gives you some cover in the case of being accused of theft and you don't know if she would be the type to make an accusation.
if something is considered missing from the house during the time you have had keys, it will be photo timed and dated evidence of what was sitting around and "oh that valuable lock on the wall", was deffo there in the time you had a key and when you put the keys in letterbox for her.
The timed and dated photos also have your back if and I hope not, that the home was broken into between you giving the keys back and her return home. As it evidences what was there at x date, and if x was missing at y date when Ndn returns home.