I can see you are very angry from your wordings which I totally understand.
What I think you have to do immediately is termination of your current maid. Obviously, your current help doesn't like the duties to take care of the disable eldery, so better send her back as not to drive yourself crazy by seeing her 'unwillingness'. On the other hand, since her nature is not caring elderies and not willing to learn, it's 'waste gas' to teach her here, wasting your time and mind only.
I hope you can find a good helper ASAP, but not by this agent again...
On behalf of BK moms, thank you very much for telling us such a BAD agent in HK~!!