Mother in laws.

Is it right for your mother in law to harass her daughter in law? My fiancé's  mom told me that she is gonna make my life unsafe and uncomfortable until we move out of her house. It all started because I told her if she is still with her husband when my baby is born then i won't bring my baby over to see her ever. And she just said that's fine that she didn't care. Keep in mind her husband is a drug user and dealer and his mom does drugs too. What should I do l? I haven't left my room because I don't feel safe walking around the house.