Dealing with a toxic step mil

My husband's step mom drives me insane. She is an extremely toxic person who I can't stand. She has blamed me for my miscarriage. Blamed me for being SA'd in my childhood and tells everyone I'm a slut. She was also extremely abusive towards my husband growing up. His mom died from a drug overdose and she would tell my husband his mom never loved him and burn him with cigarettes. She told his dad he was self harming and had him taken to hospitals and was an absolute evil person. But his dad has made it clear if he had to choose, he's choosing his wife. So if my husband wants a relationship with his dad, he has to have his step mom around. Part of its complicated because his dad is in a wheelchair and depends on her for stuff so that may be part of why he stays. My husband doesn't want to lose another parent but I really can't be around her. She found the hideaway key to our house and just came INTO our home while we weren't there. When I just had our first baby and she tried to be in the delivery room. Has said things about our son not being his because me and my husband have brown hair while our son has red hair. Our son passed away from SIDS back in August and she MOCKED us about it! Still torments my husband. I've spoken to my husband. She brings us no goodness in our life but my husband doesn't want to lose his only living parent. If his dad cares so little about him to stay with this awful woman is he worth losing.