She won't admit she's anorexic...
I think my friend might have an eating disorder. She is a little chubby, but not overweight at all. I know she isn't close with her parents and they have not had a positive impact on her body image.
She is now obsessing about calories and all the weight she has lost. She is kind of stubborn and I don't think she would ever tell anyone if she was anorexic. Since she doesn't have a good relationship with her parents, how can I offer her support?
Girl, you are such an amazing friend for not only noticing that somethings up, but figuring out how to handle it. She's super lucky to have you around. I agree that it sounds like somethings up with your friend, and I'm really sorry about that!
Letting her know that your there to talk is the first step in gaining her trust. Tell her that you love her no matter what size she is and that she can trust you with any secrets. Why not read up on eating disorders so your armed with knowledge when she comes to you? You can find some information RIGHT HERE. If she refuses to chat with you, even after you've given her a few days to think about it, it might be time to tell a counselor at school, or a teacher you trust. They can take her aside and figure out the situation, and if it's very serious, they'll help her seek professional help.
I know it's frustrating to feel like that's all you can do, but till she learns that she has a problem, the situation is out of your hands. Just seeing that your friend needs your help is a great place to start.