It sounds as if you have alot of drama going on in your life. I dont know how old you are but often times, friends are just people to pass the time with. Meaning that you more than likely are not going to having a long lasting relationship with most of them 10 years from now.
If this girl was a friend or even cared about your feelings at all she wouldnt have threatened you the way she did. It seems that the more you try to make things better with this the worse they get. I agree with ELB that you need to try to develop new friendships with other people. Maybe some time and distance from this situation for both sides would be best.