Sorry to hear of your problems, Once blind. Alzheimers is very difficult to deal with and your Mother will need a lot of help.
I heard an interesting programme on hearing voices. When you look at something, it takes a small time for the brain to process the information. Similarly when you hear something it takes time (but a slightly different time) to process the information. Then the brain puts the information together to make sense of it.
It also takes time to process thoughts, which the brain has to link to other information coming in. The timing of all of these processes is only milliseconds.
In some people the linking together of all this information is faulty, so that someone may think that a thought they had was not created by their own brain because the timing of the processing was slightly out. It is nothing to do with outside interference by demons.
After all, the brain is only a piece of meat so it is amazing that it works at all.