My mother in law is a constant trouble maker. She is tearing my family apart. How do I stop it?

My mother-in-law is constantly "butting in". We have a blended family. I have two bio kids w/ full custody, and my husband has two bio kids with full custody. My kids consider my husband to be their daddy, and his kids consider me their mommy. She is so jealous of this. She is constantly trying to "lure" my husbands kids away from me, by bad-talking me, and spoiling me. She doesn't talk to my children, no "happy birthday" calls or anything (my son just turned 13). My parents have fully accepted my husbands children, and treat them as they treat mine. My husband though is such a "momma's boy". He constantly makes excuses for her, and will not stand up for me. She has actually gone as far as to put me in jail, because I was trying to stop my husband's bio mom from taking him. The bio mom came to town after not seeing him for years. She wanted to take him. My husband was out of town, so I made the decision, to tell her "no". My mother-in-law called the police, and told them that I was trying to stop the bio mom from seeing him (the bio mom is a crystal-meth addict). The police arrested me, and put me in jail for the weekend. My husband came and got his son, and he's o.k. Now my husband expects me to "play nice" with his mom, and I can't take it anymore. I love my husband so much, but enough's enough. I have epilepsy, and migraines, and they are out of control with all of this stress. I DO NOT know what to do anymore. PLEASE HELP!!!