Battles with digestion

My daughter has been fighting a losing battle with regularity. Frankly, at this point I am at my wits end. We have followed the advice of the doctors and friends and the internet. Still we seem trapped in a cycle of constipation. I feel so bad for her and I can't help feeling responsible for her problems. Our doctor tells us it is most definitely her diet - but she eats fruit and veggies and wholesome stuff. We have tried to stay away from tricky fruits like bananas and we took all freeze dried fruits out. We have even tried some of the wackier things from the internet - Karo syrup in her milk, snacks of fig newtons, pear purees, boiled prune water... still, the cycle continues. We try to eat food made from scratch (fig newtons being an exception). So, I am at a loss. My husband wants to go to a new doctor and get a second opinion. I just want her to feel better. Anybody got new advice?