Trust me, you have NO fault in this! There is nothing that you could have done that would have changed anything. And there is nothing that you can say or do now that will stop her. I don't mean to sound negative, but this is a very serious thing that is way deeper than something you can fix. What you can do is love her! Never make her feel like she is strange or weird. Never make her feel bad for what she does. I can almost promise you she feels plenty bad enough. And don't try to tell her how much she is hurting her body. I can guarantee she knows that too. You could ask her if she would like you to help her with accountability. But if she doesn't, then don't push the issue. And don't take it personally if she doesn't want to speak with you about it. Do try to get her to speak to someone, and encourage her to get help. This is just a delicate issue. You want to help her, but you don't want her to shut you out. You sound like a GREAT friend. Just keep being that... and pray. I wish you the best.

Like the above poster said, just be there for her...I know first hand what your friend is going through, and it is very much so hard to come out and talk to somebody about this. If she decides that she wants to talk to you about everything, just be there and listen...If there is anything else that she wants you to do, she will let you know...it just takes time.
I hope the best for your friend and you too...good luck!

and keep being such an awesome friend;)