I have Dad's POA since 1998 and now he's wanting a caretaker who has known him for 8 mo. to have it. What should I do?

He's on meds for dementia. He has been in and out of nursing homes and recently I moved him into my home in Miami and hired a full time care taker who lives with him - he is on a limited budget and when I hired her we agreed on a salary, however now she has been asking for a raise and when I say he cant afford it she goes to him and conveniences him that he can afford it and that I am the one not making this happen and she might have to quit - and if she took care of his money he would have so much more. It has become a real issue and I am worried that my dad might be able to change his POA to her and change all of his income from SS and retirement into her account. He is taking advantage of his situation and needs to be stopped. He is currently on meds for dementia and Alzheimer's however his doctors have given him test and say he has passed them.... My dad is very good at pulling together all his memory abilities when he needs to pass these test, however he cant tell me what the doctors have said or what meds he is on, or even what he had for lunch or dinner - I am afraid he is in a predatory situation and I cant seem to do anything to prevent this. He lives in Miami and I live in the panhandle of florida - what should I do?