Skinny and kinda bony is not at all usual for old rabbits -- that happens to either sick or ill-fed rabbits. The moment it was noticed that her body mass was decreasing, she should have gone to a vet for a check. It is not normal for older rabbits to just get skinny without an underlying problem.
Any change in poos is also a huge red flag. If poos are not normal fully formed round balls of consistent size, then something is wrong. This would have been further indication that she had some health issue going on.
Refusing food is another huge red flag (flag #3). Any rabbit that refuses food they normally eat is in dire situation and this would also (by itself) warrant a trip to the vet.
Hind leg paralysis can be caused from any number of health issues -- illness, parasites, bacterial infection, trauma, etc. This is not surprising given the fact that 3 prior and huge health warnings had already indicated that she had at least one, if not more, serious health issues already ongoing.
I doubt this is what you wanted to hear, but I assume you wanted the truth. I'm afraid that based on your description of her, that she did not just simply die of old age. She had numerous health issues and numerous physical symptoms of those health issues. Any one of those symptoms should have triggered a trip to the vet.