How do I get my ex out of my life forever?

My ex is a complete psycho. She told MY PARENTS she was pregnant, causing friction between them and I. They wanted me to do the right thing, which I did not wanting too. She had a miscarriage, turns out she was never pregnant or miscarried. She's just crazy. We were together for 6 months at this point so I never knew she was crazy. I guess I believed all her lies. I'm 29 now and we got married at 24. I tried to make it work for 2 years before finally filing for divorce when I learned about the lie. Our divorce was finalized almost a 2 years because she refused to show up for the court and eventually the judge just signed it because he lawyer said she was "mentally ill." It was a chaotic experience. I've been with my fiance for a little over 3 years and she's pregnant which my ex knows and she tells me she wants to kill her and our unborn baby and that should have been her and not me and my fiance. I've called the police but they told me I don't have enough evidence to get a restraining order. I'm running out of ideas? I definitely don't want her near our child. Help?