Family estrangement

Jordan
I haven't spoke to my mom in over 5 months and I'm expecting my second child. 
We've always had a complex relationship. But last year it ended up in police being involved and my sons father refusing to allow contact to our little boy. He thinks she's too volatile and dangerous to be around us. 
We live in the same town with a very small population. She's going to see me pregnant or find out through social media. Even if I keep it to myself my partner is obviously very proud he's going to be a dad and his family are also excited.
We, as a couple, don't feel she has any right to be in this child's life. I'm just concerned about how she's going to react. She's tried to have my son taken away from me, she's spread rumours about me having diseases and STI's and tried to get me fired from my job.
What new lows will she sink to? I'm already stressed out thinking how she's going to attack us next.
Has anyone else been through anything like this with family members? Any advice would be appreciated.