How do I help the most important person in my life?

She needs to realize that eating crazy like that won't make her skinny. The way to lose weight is through eating right and exercise. When you go a day without eating, your body isn't sure when it's going to eat next. So when it finally gets food, it immediately stores it, and your metabolism goes down. But if you eat like 5 small meals a day, your metabolism goes up, because your body is constantly having to burn the food. Maybe you should get a cheap membership to the gym, and you both can go together a few days a week. Also, drinking like a gallon of water every day. This is the best way to lose weight and to get in shape.

This is a tough one. I've battled an eating disorder for the past 6 years of my life and it's a touchy subject that should be treated with pins and needles because anything you say can push her away. Don't pressure her or lecture her. She's not full blown, out of control, EDed yet so you CAN help her but you have to go slow and sweet with the help. Like the guy below me said, suggest going to the gym together. Tell her to eat about 1500 calories a day and you both can work out together 3-4 times a week. This is a healthy way to stay in shape. She's lucky to have such a caring and loving friend. I wish I had someone to support me through all my issues and she's really going to appreciate you being there for her.
Also keep in mind that not eating or having issues with food sometimes has nothing to do with weight even though it may seem like it, try and see if there are other things going on in her life that may be causing her to manifest it through this sort of unhealthy behavior.

Well, I use to starve myself and run 2 miles a day to look good for a jerk. She has it in her head that she is not a perfect size. Can you explain to her that water and fruit 3 times a day is healthier than starving herself? Fresh or steamed veggies. You can tell her she will actually gain weight by not eating a well balanced diet. It is crucial to let her know she needs lots of water. You could start a work out program with her so she has a buddy. I feel for you. Its a terrible place to be in. Support her, just try to tell her she can hurt herself. Good luck!