She must be responsible for her actions and their consequences. Avoid setting expectations you cannot or will not keep. You will be a better friend by not giving in to her excuses or being tricked by her explanations. People who have recovered say it was critical that their families and friends continued to express their concerns, over and over, with love and respect. If your friend has an eating disorder, she needs professional help.
Recovery is a process.
It involves help from a variety of professionals in the medical, nutrition, and counseling fields. This could be a very stressful time for you also. You should not feel responsible for bearing this troubling time alone. Thanks for believing in your friend. There is hope.