Try not to blame yourself, your friend still needs your help and support and you can't give her that if you are feeling guilty. We all make mistakes in life, we have to learn from them and move on.

I haven't won the lottery yet.
Are you still feeling guilty?

Just checked the lottery results and i didn't win! Oh well, it was still a pretty great day.
Of course she's not mad at you, you love her and care about her and she feels exactly the same about you, true friendship like that is the greatest thing ever.

You know, at the end of the day, you don't really need to feel guilty, your friend just needs help, and its probably more help than you can give. One big thing that people with eating disorders have trouble with is attention, they seem to derive some kind of pleasure out of the attention and sympathy that they get from people. I think its part of the illness that they seek attention in a negative sort of way.

you shouldnt feel guilty, its not like you did it on purpose.
Just be there for her and help her when you can.