Final answer:
The girl who is not eating well and has significant weight loss without body image disturbance is most likely to be diagnosed with Avoidant/restrictive food intake disorder (ARFID), not anorexia nervosa, since she does not fear weight gain or have a distorted body image.
Step-by-step explanation:
The most appropriate diagnosis for the young girl described, who is not eating well, exhibiting significant weight loss, not growing properly, and lacks interest in food without any disturbances in the way her weight or body is experienced, is Avoidant/restrictive food intake disorder (ARFID). Unlike anorexia nervosa, individuals with ARFID do not have a distorted body image or an excessive fear of gaining weight. In contrast, anorexia nervosa involves severely restricted food intake due to a fear of gaining weight and a distorted body image, which is not the case with the girl described in the scenario. Given that she does not have a body dysmorphic disorder or an intense fear of weight gain, and there is no indication of binge eating or compensatory behaviors seen in bulimia nervosa and binge eating disorder, ARFID is the most likely diagnosis.