Help! My MIL

My MIL is nice and helpful at times but is a passive aggressive bitch. (Not getting into it on this post) but I refuse to leave her alone with my 9 month old.

When he was 3 months old he started rolling and she was holding him put him on the changing pad then walked away and sat down in a chair on the other side of the room. My husband and FIL were in the room and I was just entering when I saw this, I quickly walked over to my son and my FIL walked over & mumbled "oh, I was just going to get him. "

The other day she put HER finger in HER mouth then into my sons mouth to feel his teeth. As so as I saw it I said. "Mimi, don't do that. " to which she replied "why. " I was so mad that I didn't know how to respond without screaming bloody murder. She's sick alot because she's constantly licking her hands while serving food. She had pneumonia for 2 months after my son was born.

How should I approach her, I don't trust her alone with my son. I don't want to hurt her feeling but I don't know how else to cover the issue. Any advice would be welcome.