How Can Abdominal Bloating And Constipation Be Treated?

Hi, My daughter is 15 years old now, a 25 week preemie that had Grade iV intraventricular hemmorhage at birth and among the many surgeries had a Nissen fundoplication. She is a toddler in mind now, runs around, repeats what we say and is generally happy but has a lot of bloating, gassiness, constipation, still not toilet trained etc. We have changed diets, put her on laxatives, etc. but the gassiness and the bloatiness is always there and she can t burp. We are considering reversing her fundoplication. She eats soft foods, loves to eat, has good appetite generally and I don t think has reflux issues anymore. Please advice. Thanks, Uma