Final answer:
Katie likely suffers from anorexia nervosa, an eating disorder where individuals consume very little food, fear gaining weight, and have a distorted view of their body weight and shape.
Step-by-step explanation:
Katie seems to be exhibiting signs of anorexia nervosa, an eating disorder characterized by eating very little, the fear of gaining weight, and having a distorted body image. People with anorexia nervosa see themselves as overweight even when they are underweight, and often engage in excessive exercise to lose weight. This disorder can lead to serious health problems, including malnutrition, bone loss, heart failure, and potentially death.