How do I tell my bio mom to leave me alone

I recently met my bio mom last month and... I want nothing at all to do with her... I didn't want to keep her, my sister did and honestly my sister even regrets this... There are just so many red flags than I can count and yeah just no... But idk how to tell her I no longer want to see her because she is crazy and violent and will probably get violent with us.. I just want things to go back to normal with my dad and REAL MOM (dad's wife). Not whatever psychotic mess she's bringing into my life.