My best friend has been cutting since 2010 and she only told me again a few days ago. She has shown her scars to me and there all over her arms upper leg and lower legs and there is also another person I my school that does it as well and I feel like their cutting buddies and to make it worse she said she does not won't HELP. I am really scared because we are only year 7's. One of the reason why because I and the other cutter were fighting and it made her depressed. I feel like it was me who has made this happen.

You are too young to 'help' and can't anyway - an adult has to. Tell your parent(s) or a teacher.
Has it occurred to you that when she shows you her scars, she is asking for help, while saying she doesn't want it? That isn't fair to you, and you should tell her so. Same with the other one who you feel guilty for fighting with. It's always best to avoid fighting, but what people do in response to a fight is mostly based on their character and personality, who they are to begin with, not what happened in one incident. I drown my anger and sorrow in cookies, or I put the cat and dog outside even if they are sleeping, or I do some dishes, or take a nap. We all have our responses.

You must tell your parents or your teacher.

Cutting one's hair is tolerable, but cutting the skin is not. It hurts, emotionally as well as physically.

Cutting one's hair in no way compares to "cutting" as self mutilation.

Absolutely agree - this is a problem for adults to address, perhaps a parent, counsellor at school, an adult who will listen.