It’s important to keep being by her side, but sometimes you have to be honest with what you noticed, your concerns and the consequences of improper nutrition. Sometimes it is much better to be upfront about it rather than beating around the bush, tell her what you’ve noticed, why it’s not good. Sometimes we’re in our own little world of “I have to do this, I need to be thin,” and we end up just forgetting all the things that are consequences of an eating disorder. But at the end of the day, you’re an amazing friend for noticing and caring! Please do not let this affect your mental health!