I still feel guilty about all of the needless suffering my parents went through in the 6.5 years between my diagnosis and the start of effective treatment. I do know it wasn't my fault- I'm getting a teensy bit better at that.
But a diagnosis of an eating disorder in a child is often confusing and (when you start reading) kind of depressing. Don't get me wrong- an eating disorder is a life threatening illness. But there is also hope, and that's what we all need to cling to as the world gets tipped upside down and shaken like a snow globe.
It is not her fault. She is not choosing to do this, to feel this way, to think the way she is. It is a disease - a brain disorder.
It is not your fault. You did not cause it and probably could not have predicted it (unless you were an eating disorder specialist). It was a genetic predisposition that got set off by something (probably malnutrition or energy imbalance due to exercise).
It is fully treatable. With quick and assertive intervention, full nutrition, a lot of emotional and practical support, and time (many months) your daughter can not only recover her health she can be protected from eating disorder in future.
You will get a wide variety of clinical advice. Much of it will be mutually-exclusive. Some of it will be absolutely wrong. The world of eating disorder treatment is undergoing a massive change and that means you have to seek and secure the best care possible. Do not depend on clinicians to tell you what other clinicians offer.
The best evidence for effective treatment of adolescents living at home is "Family-Based" or "Maudsley" treatment. It is not widely available. Some old-school clinicians even advise against it. Research this approach, as others have said, and make up your own mind. It is worth travelling further to get the right treatment for your family than staying close to home and getting inadequate care.
You will be okay. Your daughter and your family can beat this. Do not believe anyone who tells you this is hopeless or that you should sit back and wait or watch - they are wrong.