Insurance companies

I am watching The Doctors right now. There is a girl on the show who has a problem where her breasts are growing and won't stop. She is 11 years old with a 50 f cup. Insurance is refusing to pay for the treatment she needs and I'm wondering (if there are any insurance adjusters on here reading) what exactly is the process u go through to decide whether or not a treatment is necessary. Even if the doctor is saying it is absolutely necessary. Could someone explain please