hey babe, so so sorry for what's going on with you, it really sucks. and i know how you feel. it is bad enough when a friend is mean, but for them to make themselves into the victim is the worst and lowest thing and is really unfair and difficult to handle, so i feel for you. sorry you didn't get into the uni you wanted, it seems unfair that a bitch like her would get it when you didn't, and she should not have rubbed your face in it. that is low, low, low. sorry for you.
I think it is true that you should talk to her though, because its the only way to get rid of all the misunderstandings, especially from people who aren't directly involved.Maybe writing a letter would be easier than face to face, because it will mean you can get your feelings across without her interrupting or antagonising you so you lose your temper which is not constructive. You also won't leave anything important out. You are NOT bullying her and its so sad that you feel guilty about things that were obviously her fault. If your teachers tell you to look after her, maybe try and simply explain as calmly as possible that actually you are trying but are feeling overwhelmed by difficulties between the friend and you at the moment, and that you are trying to sort them out.
the people accusing you of bullying her are wrong, and have obviously misjudged the situation. I would say that they probably aren't having as friends, but that is completely unhelpful, and it probably isn't their fault anyway. try talking to them as well, explaining how hard it is for you at the moment.
The only thing else i can suggest is to maybe confide in another friend. feelings can get so pent up and scary sometimes that you do feel like you are going to burst, believe me i know. sometimes it helps just to talk. whether its to a friend (the most helpful i find), to a counseller, even you favourite teddy bear, or maybe a diary.
I hope i have helped a little bit, im so so sorry that you are going through this and i hope you manage to sort it out. be strong.