What are the 3 main functions of the digestive system

An adolescent girl (ms. c) is admitted to your medical-surgical unit for diagnostic evaluation and nutritional support related to anorexia nervosa. she is mildly dehydrated, her potassium level is 3.5 meq/l, and she has experienced weight loss of > 25% within the past 3 months. ms. c's self-esteem and weight have gradually improved, but she continues to refer to herself as "fatty." she is able to appropriately verbalize an appropriate diet and exercise plan. what is the priority nursing diagnosis?