Eating disorders are potentially life threatening, it's important that she speaks to someone. She took a step in the right direction by telling you, people with eating disorders don't just come out and say something like that, eating disorders are usually very secretive. She realises that she has a problem, and she confided in you, that's great. To help her get through this, your support will mean a lot to her. Get her to speak to a doctor as soon as possible, she is harming her body with her eating disorder, she needs to get checked out. They will be able to offer help. As horrible as it might seem to her right now, it's the best option if she wants to get better. Speaking to her family would be a good idea too. The more support she has, the better.