AIBU to think that your own bedroom is a private space and as an adult your parents should respect that?
My mother is staying right now and to put it mildly, she's extremely hard work. My bedroom is private to DH and I don't expect to find her in there 'tidying' or whatever else she says she's doing. I would never go into someone else's bedroom unless expressly invited. Just because she's my mother, doesn't give her the right to do what she wants. She drove my SIL crazy doing the same thing when she stayed there. She also knocks and then walks straight into rooms and sees nothing wrong with doing so.
So, I have asked her not to go in there (nicely!) and she's gone off in a huge huff, muttering something about 'if you can't go into your own daughter's bedroom etc'.