My Grandma is physco, what should I do?!?

Ok, my Grandma is 85 years old, she is an immigrant from Germany and has lived through the time of Hitler. She talks to herself like randomly. My Mom says she has dementia. And She has thyroid problems. She flips out randomly too, like after my Grandpa died she moved in with me and my family and she has a rental house she rents out to people. So when something doesn't go her way or she does something to piss my Dad off she says, "I'm moving back! I'll take all my money away. You will end up on the street." Yesterday my Dad bought me a bookcase and I've wanted one since i was really little. We put it at the foot of my bed and put all my books and photos in it. She apparently didn't like where it was so she tried to move it and it broke into many pieces! I really don't want to bring my boyfriend home cause of my crazy Grandma, and I just don't feel any love toward her anymore. She's said awful things to my Mom and my Dad and I just can't deal with it anymore. What can I do??