I was like that as a baby, and continued to suffer until I was 18, went away for college and started taking care of myself. I went through my entire life with daily pain like your daughter, constant congestion,
bloating, abdominal distention, horrible gas pains and irregular stools, join pain, and other conditions, all of which went away on a dairy- and
gluten-free diet. I can't believe I went my entire life in pain just from the types of foods I was eating. Even things we consider 'normal' or 'healthy' in the modern diet are highly unnatural. Test out variations in your daughter's diet, she could be intolerant to dairy, gluten or fructose. It's overwhelming to look into, but please do it for her. My mom was told exactly the same thing as Dr. Das said above, and as a result, I suffered for 18 years not only with pain and constant
fatigue, but the body-image issues from a belly that looked 6 months pregnant didn't exactly help. You can get her tested, but the tests are not as accurate as testing out elimination diets yourself (while making sure she's getting a balanced diet, of course.)