I'm going to reprimand my mother in law
Why do you want to reprimand your mother in law?
She's really rude to me. I think she should know her place.
Your mother in law sounds very rude, but you shouldn't reprimand her. You will only cause more problems with your spouse and your spouse's family.
I have to do it, my future son doesn't deserve to have her as a grandmother.
If she's being rude to you, being rude back isn't a good solution. Try to be respectful and talk to her and your spouse about ways you can get along better.