I get several emails a week from people who are trying to help a friend, loved one, family member who is showing signs of an eating disorder. They want to know how to approach them, what to say, etc. This was my response to a lady today, who is trying to help her friend who struggles with bulimia and is in the Navy.

I am glad you contacted myself, and what a great friend your roommate has. When someone struggles with bulimia (like myself for 10 years) there is denial, secrecy, lies, low self esteem, control issues, isolation, and the list goes on. The first step says that, "We admitted we were powerless over our eating disorder and that our lives were unmanageable." She needs to understand that first and foremost she is powerless over food and throwing up; and with an eating disorder in her life it will become unmanageable. If she admits this then she will realize she cannot do this on her own. I just helped another girl in the Navy who was stationed on Coronado get into treatment for anorexia. Step 2 says, "Came to believe that a power greater than ourselves could restore us to sanity." Insanity is doing the same thing over and over again expecting a different result so for example: "I will not binge and purge during the week, I will go on a diet, I will stop cold turkey, I will become a vegetarian, I won't eat sweets". The thought process of someone who struggles is, I will try different ways of getting rid of my eatings disorder and this time will be different; however the result ends in over eating, throwing up, and doing the same thing over and over again.
I would recommend a site I helped create called, OneRecovery www.onerecovery.com. OneRecovery is an on line free support network for those who struggle with drugs,alcohol, and eating disorders. There is online eating disorder meetings, accountability, support, and tons of people who also struggle with an eating disorder so your friend won't feel alone. Also I would tell you that you can't help someone who doesn't want to be helped. You can't work harder or want it more than the person with an eating disorder. Your friend needs to reach a bottom, and when she has a moment of clarity where she is sick and tired of being sick and tired, you can be there.
Let her know you are here to support, talk, and be there when she is ready to face the addiction/disease. Your friend can always email or call me when she is ready, but she needs to make that decision for her. You can let her know you are going to love her until she can love herself; and although you don't struggle with an eating disorder, you can understand how it feels to need something to numb the pain, or to want to check out to not have to deal with issues. The eating disorder is her coping mechanism; for some it is drugs, alcohol, sex, gambling, shopping, love, etc. We all have a coping mechanism, and the idea is to slowing remove the mechanism and deal with life on life's terms no matter how hard it may be. 
I know it is hard to watch someone struggle and hurt, and our immediate reaction is to want to fix it.  Continue to look inside your self and see what changes need to be made in you, and hopefully your friend will see your growth and want to change for herself as well.