I have a MIL that makes me want to pull out my hair (or better yet, hers

).
Maybe because of my personal experience,
I am inclined to believe that the MIL is doing it for attention, to make the DIL uncomfortable, or to see if her baby boy still loves her the most.
Even if I am off base, I don't think we should scorch the OP with harsh remarks. I think sometimes people just look for a way to flame OPs. I don't mean you have to agree with the OP. Disagree repectfully, while realizing on the other side of these words is a breathing person with feelings.
OP, sorry your MIL makes you uncomfortable in your own home. I wish I had sage advice for you. However, after 18 years of marriage, mine still tries to play games.