On the pragmatic level, is the child drinking plenty of water? What is her diet like? Do you know how to test substances, foods, etc with kinesiology? Perhaps there is a food sensitivity involved.
There are a number of self administered techniques that can be shared with the child, and that she might enjoy participating in herself. This simple qigong exercise was taught by a Qigong master who was in China during the cultural revolution. It's worth a try:
With hands outstretched, palms facing down, thumbs facing inward, twist the wrists rapidly until palms are up and thumbs face out. Gently return them to the start position, and again flick them out, turning at the wrists. (For Montezuma's revenge, reverse the emphasis, flicking the thumbs in instead of out).
You can test to see if the ileocoecal and Houston valves are working rhythmically using kinesiology. Placiea palm over first the right side of the abdomen inside the pelvic bone, and then the left side, and check an outstretched arm for strength. This takes some practice as it is not a test of muscle strength but of energy flow. It won't hurt to do the corretion in any case. Oneself, one starts in a stance with knees bent slightly, which allows a deeper massage. Starting at the corners of the pubic bone where it meets the pelvic bone, massage up from pubic bone to waist, repeating 3 times. Then trace down with the thumb along the path of the pelvic bone from the waist to the pubic bone. This can be repeated daily, or morning and evening, to reset the rhymic opening and closing of these valves.
Massage the Large Intestine neurolymphatics: either side of the base of the spine, and down the outside of the upper legs. They will probably be tender, especially the outside of the thighs, but the more pressure she can stand, the better off she'll be. Also massage LI 4.
Try flushing the Large Intestine Meridian - be tracing it backwards once, and then forwards three times - on each side.
Remember too that Large Intestine is about letting go, not merely on the physical level but also as a metaphor. Further, there are reflex points to all the organs and glands in the body, all along the wall of the intestine. Does she complain of pain or tenderness, and if so where is it located? That could give a clue as to where the problem actually lies. Information about the location of the various reflexes located in the large intestine is part of Chi Nei Tsang, as taught by Mantak Chia.