I was wondering if her doctors have considered issues like bulimia/ anorexia in her. Other than this issues that may need to be considered are recurrent infections, food allergies/ intolerance, parasitic infestations etc. Without a clinical evaluation it would be inappropriate on my side to comment further. I would suggest a detailed evaluation by a gastroenterologist for the above mentioned possibilities. After a cause is diagnosed, it can be managed accordingly.
Hope this helps.
Welcome to the gastroenterology community! I do not think she has bulimia/axorexia for the information you provided. It could be gastroparesis which is slow emptying of the stomach. I would recommend you ask your doctor for a gastric emptying scan.
Bulimia nervosa can presents with nausea, vomiting and diarrhea in young teenagers. It is not typically a gastro issue and has psychological aspects to it, where the vomiting and diarrhoea can be self induced. These are important diagnoses to be ruled out. Gastroparesisis may present with nausea vomiting, abdominal pain, bloating etc. However the symptom of diarrhea may indicate an alternative diagnosis.
I totally agree with you Dr. Kaul. Talking to a 16 year old about her "habits" is imperative in this situation. I don't feel it would hurt her psychologically as it is part of the diagnosis process. Anorexia/Bulemia cannot be ruled out with the information given and must be considered along with all other possibilities. This condition is very common and especially in the teen years.