Although I don't think that I would have complained about that maid laughing at your niece, which I know you did not say that, I am just stating it, I would have been angered by her stupidity for the incident, you could have sued them, then I don't believe that she would be laughing anymore, all the way to the unemployment line.!
A long time ago, I had an incident similar to yours, it was not at a hotel though, it was very horrifying to see, how many people actually thought it was either funny, or they were indifferent.
If I see someone just slip o.k. I might and probably would giggle over it, I believe it is a part of human nature, however to laugh at someone that is handicapped at the time? No way!! that is just so cold, mean, nasty and low down, low class too! stupid,stupid rude maid! she probably just hates her job, and so does not care about anyone else there, just a thought.
I hope that you reported the fall to the office, and received room credit or something else of value. when one falls down, it can be really very painful!
I am angry at that woman for laughing at her, that is adding insult upon an already injured person, then is adding on top of that more physical pain!