Yeah, I went through this with a friend last summer. It was absolutely horrible. My friend, who's 5'2 and 90 frickin pounds (!!!!!) thought she was WAY overweight. It's like she looked at herself in the mirror, and just saw like 50 pounds extra...I don't know
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It was very emotionally draiining for my friends and I, b/c we would try to convince her that she actually was TOO SKINNY (unhealthy) for her height, yet she would just say, "But you're just SAYING that to make me feel better."
She exercised constantly, like 4X a day. After eating carrot sticks for lunch, she would hit the gym at our school, do weights, etc. ACtually, she was so tired and fatigued that she would faint after doing too many reps on the weight machine.
My friends and I didn't know what to do at all. Teachers even approached her and tried to talk with her and explain to her that she was suffering with anorexia. But, she would deny it and, one day, blew up finally and told us that she was the one who was in charge of her life, and that we had no right to tell her what to do and whatnot.
We told her parents, but her parents denied it too (I think it's cuz they didn't want to acknowledge that their daughter had a problem). Finally, teachers and administrators arranged for a parents' conference, and made them see finally what their daughter was suffering. Soon, my friend was enrolled in therapy and also, was admitted to the hospital.
She spent a month in the hospital b/c she was SOOOOO undernourished...she lost about 30 pounds in a very short time while she was an anorexic. She spent months in therapy (and still goes today). Before she was admitted to the hospital and therapy, she even considered suicide.
So basically my point is, NO MATTER WHAT YOU SAY, she won't listen. You really have to get the attention of authorities...unfortunately, my friend had to be FORCED to enter the hospital. All you can do for your friend right now is get help from those who can do something to help her. Also, be prepared for a very rough, emotionally-taxing time, b/c it was sooo frustrating for my friends and I, b/c no matter what we said, she just would not listen.
I'm really sorry that your friend is going through this...I just really hope that something can be done for her...the sooner, the better. Good luck...