Katie weighs less than 85 percent of what is considered normal for her age and height. yet, she sees herself as too fat and starves to become thinner. katie most likely suffers from:

Katie suffers from anorexia nervosa.
Katie is anorexic - she is suffering from a mental disorder which is making her see herself and her body in the wrong light and she cannot see what she actually looks like. Therefore, she is starving herself in order to become thinner although she is already extremely skinny and it is severely ruining her health. 

Idkk take a guess i am no