Why was she in your stuff? Is your stuff out in the open or in a separate room? I don't understand why anyone would get into other people's business, family or not. Now you said that you don't say anything because you'd be the nasty one. I think you really need to set boundaries. Had to do it with my MIL. We get along famously now because she knows how far she can go with me and where she better not tread.
Hope you find your crumbs.
Want me to come over and set her straight?