Monster-in-law issues

I am engaged to a amazing guy, however, his mom is not so pleasant. She came to visit last month and she followed him around the whole time. If he went to the gas station for a quick moment she would run down the stair to follow. If he went to work to get some papers signed for a little bit. She would ask to go. Then she pulled all the stuff out of the kitchen drawers and put it in a trash bag. Then put it in the middle of the floor. Let me say that it is my apartment that we are staying in.  My fiancé is not on the lease and I pay all the bills. She then questions him about if he should marry me and telling him lies that she never felt welcome at my home. When I asked her if she wanted to go and look at wedding venues with me she act like she didn't want to go and she didn't. Then she keeps saying things like when you guys get your house I am going to move in with you guys. I am thinking heck no! She acts like me and her son are not really going to get married. Although, we are getting married in May 2017. She rearranged my kitchen without my permission. My fiancé keeps saying I have nothing to worry about and that she likes me but I don't see it. I feel like she just want to live, eat on us & be in our business. She is on welfare so I think she want to just live off of us since we are getting married and we both have good jobs. I need some advice and help. What do I do?