Okay, so there's a couple misunderstandings you made here about the science, OP. The MAOA gene has to do with how our body handles certain neurotransmitters, specifically the feel-good chemicals in our brains. A MAOA low gene type is associated with violent behavior, however, it's not a strong association. Assuming everyone with low MAOA type is a serial killer is as faulty as assuming eveyone who's poor is a criminal. There's some level of influence there, but it’s not a huge amount and it certainly isn't enough to make everyone with low MAOA genotypes a serial killer. You were very unlucky.

That said, move away, change your name, keep in touch with the police only. It isn't because of her genes, but she's still a killer. Stay safe.