We are sorry to hear about your friend's struggles with food.  It sounds like she may be suffering from an eating disorder.  Eating disorders are very difficult and can be a huge obstacle for the people who suffer from them.  We hope you can provide your friend with the following websites.  Hopefully she can check them out, learn more about herself, and decide that she needs to change her habits...

www.something-fishy.org
http://mirror-mirror.org/eatdis.htm

Being friends with somebody who has an eating disorder is very difficult.  The best thing you can do is continue to monitor them and continue to let others know.  Also talk to your guidance counselor about how you can be a good friend to her.  She will have a lot of knowledge of how best to help them.  You are a good friend and it's great that you want to help.  Tell her you are worried, tell her you care for her, and tell her you will go with her to get help.  We are sorry you have been placed in such a hard situation. 

Please give yourself a break from focusing on this all the time.  Make sure you take time for you each and everyday by doing things you enjoy.  If you focus on her all the time you will burn yourself out, drive yourself crazy, and then you won't be of any help to her or anybody else either.  Before we can help others, we need to take care of ourselves.  Please take care!

Counselor, Dominic