Do you get along with your Mother in Law?

Mine has been a Monster In Law from the day we met. She's compared me to my husbands ex, (in front of me) is a drug addict, and has threatened to tell lies about me to have my kids taken away from me. My husband has been fine with cutting her out of our lives, but recently wants to start seeing her again. I can't say no because it's his Mom, but at the same time I can't stand to be around her and It's very hard to forgive someone who has threatened my kids!