What should I do?..............?

I know it's stupid to do any kind of business with family. But for about 3 years I have been living in a house with my adult niece. I have been giving her 800 dollars a month for a slapped together room in the garage. I get paid twice a month so I pay half on one check and half on the other. My son was supposed to share a room with her son and most of the time the door is locked so he ends up in my room. She takes parts out of the stove so I can't use it and throws my leftovers away whe she feels like it. This last check I put the rent under her door as I have a few times in the past and suddenly she never got it. She knows I haven't been able to save to move. She's told everyone in our family that now she has no money for anything but in the past week she has gone out of town twice and gotten take out all but one day. I know there's going to be another blowout cause I do not have another 400 to give her. Should I just lock my door and threaten to call the cops if she doesn't back off?h so I pay half on one check and half on the other. My son was supposed to share a room with her son and most of the time the door is locked so he ends up in my room. She takes parts out of the stove so I can't use it and throws my leftovers away whe she feels like it. This last check I put the rent under her door as I have a few times in the past and suddenly she never got it. She knows I haven't been able to save to move. She's told everyone in our family that now she has no money for anything but in the past week she has gone out of town twice and gotten take out all but one day. I know there's going to be another blowout cause I do not have another 400 to give her. Should I just lock my door and threaten to call the cops if she doesn't back off?