My elderly mother in law lives with us and she imagines she hears me conspiring against her?

My wife adores her mother. Her mother has been diagnosed with the early stages of Alzheimers and she thinks she hears conversations of me and different people plotting against her in the middle of the night. She tried to hit me with a broom this morning when I was on my way to work at 3:00 am. She said that I had been plotting to take her to a home. I was sleeping all night since I had to be up early to go to work. She also accused the lady accrossed the street of trying to take her land. She said she heard the lady at 2:00 am in the morning in our yard plotting to take her land. My question is that is the usual progression Alzhiemers takes? Are people with this condition prone to paranoia? She is on Aricept and it is not helping her. What can my wife and I do to help her? Thank You!