Dr. Greene's Answer
Having the belly fill up with stool is more common than most people think. The scenario is so common that I created my own name for the downward spiral that leads to it. I call it the D3 Cycle (discomfort, dread, delay).
How Does the D3 Cycle Start?
Children can enter the D3 cycle at any point. Sometimes it begins with an uncomfortable experience passing a hard stool created by a change in diet or a brief illness. Sometimes the starting point is simply the fear of sitting over the gaping hole in the potty to poop. Sometimes children are engaged in playing and choose to ignore the urge to poop, holding the stool in just to delay interrupting a vitally important game.
Whatever the starting point, they end up having a painful experience. When the next urge arrives, the child decides to delay going to the bathroom in order to avert what happened last time. The longer she delays, the firmer the next stool becomes. When she finally does poop, the event is even more uncomfortable-confirming her fears. What she dreaded was true!
She vividly learns from this experiment, but it’s the wrong lesson. So next time she is even more determined to hold in the stool. Discomfort leads to dread; dread leads to delay; delay leads to discomfort. The rectum stretches internally so that more stool can be held, and soon urges to defecate are not often felt. The D3 cycle becomes a powerful trap.
How to Stop the D3 Cycle
But this trap can be undone. Kids should not have to learn to live backed up with stool.
You said that she has been on a program to reverse this for 3 weeks. That sounds like the right place to begin. It can take a while to get the bowels regular. Once kids are having daily soft stools, it takes another 2 weeks for the intestines to shrink back to normal.
Cramping pain during this process is not unusual. If the pain persists after the stool problem is resolved, a long list of other possible causes should be considered. Food intolerances, celiac disease, inflammatory bowel disease, parasites, or other infections could cause it-to name a few possibilities. Further workup may be indicated to find out what else is going on. Children with these conditions deserve to have them identified and treated.