somebody plz help me.

If you and your friend are fighting i suggest you sit her down and talk about it, find out how this got started and figure it out together.
However if she's threatening to beat you up and your frightened that she will do, you MUST tell your parents. Especially if your friend will actually hurt you.
But if she's just threatening you over the internet or on your phone, i wouldn't worry about it too much. Just block her number or change numbers on your phone and ignore her.
If you go to the same school try to stay away from her as much as possible. If you sat seguinte to her in class go see your teachers before the lesson starts and explain to them what's going on and ask that they place you to sit somewhere else. This would also give you the advantage of getting to know someone else and probably becoming their friend.
If this friend of yours is leaving you alone at home, but bullying you at school, you MUST tell your headmaster/teacher or another adult who will then act accordingly. If things don't get better and you actually get hurt on school property por this girl you can take legal action against the school for negligence.
If this girl keeps coming onto you at início and school and no one is paying attention, i know this may sound drastic but i suggest you should go to the police and get a restraining order. However they will ask for proof that she's stalking and threatening you, so you must keep any record of what she says or does to you. If you get cuts and bruises from her photograph them, if she says something to you write it down in a notebook, keep text messages or emails, and if you can - tape any phone call she calls you.
But you should try sort it out with her. Sit her down and find out the root of the problem. You never know, if she turns up and you both listen to each other and talk about your feelings you could end up being best friends for life :)
Good luck hun.

Is she on fanpop? If yeah, then denunciar her. If not, tell your mom and dad XD

When you say you are fighting, you mean physically? Then you should tell your parents ASAP.

There's no need to be too worried. You started por saying that she's your friend. So you either are or have been friends before. You can easily make up with her if there is a true friendship in there. But if you're still worried, just make sure to lock your doors and windows just so you will feel safe.

What about threatening her? That usually works. Or learn some moves, so that when you're fighting, you can kick her balls.