As a friend, you should take the responsibility to force her to eat even against her own will. You have to keep pushing her to eat even though she does not want to. You need to talk some sense into your friend to tell her that there is no point of starving herself.
Awww:( I am very sorry to hear that, you really need to tell someone who could help her... Or just try your best to convince her that there is no need to starve herself and she is great the way she is!! I hope I helped:)
Why is she starving herself? First make sure that she is starving herself then make sure she knows you are there for her. Don't announce it to anyone because most people don't want anyone else to know and it would feel like a betrayal of trust. If it is to lose weight, let her know that starving herself can actually slow the metabolism and make her body preserve more fat. If it is because she feels bad, help her through the situation and help her find other ways to deal with it.
Check the ABA for Anorexics Anonymous website for some potential answers if you think your friend is in trouble. You need the help and support of a whole group of people that can help you deal with this situation and answer all your questions from a therapeutic and informed approach. Your friends life may be in danger. Starving ones self is very dangerous and can easily result in death or lifetime disability! Your friend is probably very wonderful and a beautiful person, yet sadly does not realize this. Hardly any amount of reassurance from you will make much difference, unfortunately as studies have found. Please take swift action in following up on the website and the information therein.