How can i get rid of a psychotic friend?

i'm hesitantly friends with a young woman who is very hard to handle. the last time i told her we were no longer friends, she begged and pleaded with me to reconsider and then she sat in my car, making it impossible for me to leave. after an hour of refusing to leave the car, she finally got out and went back inside her house. i thought i was being nice and i gave her another chance. ever since then, she's been randomly getting mad at me for the stupidest things. i can't stand it anymore! i'm going insane! the last best friend she had left her after 3 years and got her clothes burned in a backyard bar-b-que. i have nothing left over at her house so that won't happen to me. how can i make a clean break without her going into a hysterical rampage? she knows that our friendship is up in the air right now and i need to get out for my own sanity. please, only serious and helpful solutions only! thank you