Hello ConfusedAFboutpeeps: I see this is your first post here on PC. So... welcome to Psych Central.

I don't think there is much of anything I would be able to offer with regard to the motivation behind your mother-in-law's behaviors. Perhaps there will be other members, here on PC, who will have insights they can share. However regardless of what lies behind your mother-in-law's behavior, at least from my perspective, this comes down to personal boundaries. So here are links to 9 articles, from Psych Central's archives, that offer advice on establishing & enforcing personal boundaries:

The Importance of Personal Boundaries

What Are Personal Boundaries? How Do I Get Some?

4 Tips for Setting Healthy Boundaries

10 Way to Build and Preserve Better Boundaries

10 Steps to Setting Healthy Boundaries | Happily Imperfect

https://psychcentral.com/blog/5-ways...dium=popular17

https://psychcentral.com/blog/when-p...ur-boundaries/

https://blogs.psychcentral.com/imper...ur-boundaries/

https://blogs.psychcentral.com/sex-a...dium=popular17

I hope you find PC to be of benefit.