My Jekyll and Hyde mother, how do I deal?

My mom and I have never been very close. When I was kid, she would constantly scream and yell at my siblings and I, making us all feel guilty for existing because we cost her money. Always very verbally abusive and At times she was also physically abusive. My siblings and I all moved out during our senior years of high school because we couldn't take it. I'm 33 years old and happily married now. I've basically let everything go and forgiven my mom. I keep her at a distance because she is very negative and I have a hard time tolerating her. I have short conversations with her about once a month and see her on holidays. Now, I'm pregnant and she is acting like we are best friends. She told me when the baby is born she is going to take a week off of work and come stay with me. I will go insane if she does that. I had a miscarriage back in February, I texted her and told her, she responded and said sorry, but she never called or offered any emotional support. I feel so irritated by her fake, "I am such a loving mother" act. She can also flip like a switch. My question is, how do I deal with her and this act and how do I tell her she is not staying with me after the baby is born?