This is something that requires being really, really delicate (as sun said with love). My ED began at full force when I was 16, and the friends I had at the time saw how my body was changing, how my mood was changing, how weak I was and withdrawn I was. The problem is, ED's are tricky. When we are un-diagnosed, we don't like to believe are eating is disordered. Even when we are diagnosed, we sometimes argue and fight that we are fine and this is very much normal because it IS normal to us.

From my own personal experience; my friends did what sun suggested and told a guidance counselor. It didn't end well for me. I felt attacked, vulnerable, and as though I had no one on my side. If anything, it made me remove myself further from friends and family. I felt like it was a violation.

I think having a sit down is one of the better routes to take. She needs to feel safe, loved, and respected. I know a lot of people who spoke to me like I was a child and it pissed me off something awful. I don't think you'll do that. Find a neutral place to talk (not a home, but a park, a coffee shop, some where you can have a quiet conversation) and just explain your concerns. Tell her you love her, and that if she ever needs you, you'll be there for her. And that she can talk to you and not fear judgement.

I wish you luck and I hope your friend gets help soon.