How to stop my MIL snooping through my room.

She's not even my mother in law she's my boyfriends mother it's just easier to call her that. I'm out all day tomorrow and so is my SO, we want to find a way to stop her from coming in and going through my stuff as she's really weird I don't know if she's looking for sex stuff to sniffing my panties. She's a filthy woman and I don't want her near me or my things. What are some traps to stop her or to find out if she's been in here, I recently put an empty pop bottle right behind the door before I closed it and went, when I came back the bottle had been moved so she clearly went in after us telling her SO MANY TIMES NOT TO COME IN!! Can anyone recommend anything? I don't have a camera or voice recorder, are there any other ways or any traps I can set?