Pretending the problem doesn't exist won't help either, kid.
You asked for help. Now you're afraid to address the problem. And for your friend's sake, you better show a little courage.
It's like Gungonx said, this is just like the last thread.
First, she could be going through what is called a phase. She could be doing it for attention. Let's play it safe and assume she's not.
1. Next time you see her, drag her in front of her parents and tell them what she's been doing. They won't believe you? Make them believe you. You say she's been giving her self deep cuts. They leave marks, don't they? Show them. Freaking get mad.
Get mad enough, she'll break down in tears and realize you want to help her. Then she'll realize how she's affecting others. She'll get help. That is, if she's smart.
2. Tell YOUR parents. Show them that you're genuinely concerned for your friend. Ask them if you can all talk with her parents. With her present, if possible.
The point is, you need to figure out a way for her to realize that she needs help. She is coming off as a child who's taken tantrums to a new level. She needs help.