Please help me,my cousin has an eating disorder.!?!

I have a cousin aged 15,and she is really thin. I'm younger than her,but I'm much taller. She has a problem making friends,she is shy and cynical,and a bit rude, always lazy and bored, she's not a good student (okay these are her flaws, but she is a very good friend when you get to know her and all, i love her very much and she means a lot to me that's why I'm doing this,because her parents refuse to listen -.-) . Recently she had a really bad stomachache and has vommited blood and then she went to a hospital and she sat there for a few days and when she came back home she vommited again like 9 times and had fever. Now shes better but she can't stop coughing! She is now even thinner. She always tells me that I'm fat and that I eat all the time, which is not true at all. Also she told me she hates to eat, and the fact is her mom is a horrible cook and she always refuses to tell me what she had for lunch, but I know she eats the same everyday.... potato potato potato and sausages or chicken... She doesn't like anything else,and she doesn't eat fruit. The nurses told her she doesn't have to eat a lot because she looks awesome, but believe me everyone is worried about her. My other relatives and friends from school think she is anorexic. But she doesn't think she is overweight (she just thinks that she is average and that everyone else is fat) and she doesn't have the regular anorexia symptoms. Does anyone know how to help her? Please, I'd be really grateful.