Small Intestine Bacteria Overgrowth

I have an 8 1/2 year old daughter with Rett Syndrome. Gastro issues are quite prevalent among the girls, my daughter included. Constipation has been an issue for years but daily doses of Miralax were working. In January, we had to try a generic form of one of her medications and she became severely constipated. Was never the same after that and was finally diagnoses with SIBO. After a few days on Flagyl, stools became more normal again. She has just started her third round of Flagyl as it keeps returning. She is scheduled to see a new Gastro on September 1st(four month wait) but I am wondering why we can't get this under control. Any ideas.

[boron]

Constipation itself may contribute to SIBO. When small intestinal peristalsis slows down bacteria persist in the small intestine for prolonged time and may overgrow.

Eventual obstruction within her small intestine or incompetent ileocecal valve (that separates colon and small intestine and prevents invasion of colonic bacteia into the small intestine) could be possible...The later can be checked by colonoscopy.

Sugars (fructose, lactose, glucose, sucrose...) are food for bacteria..you may search for "FODMAP diet"  

SIBO is often associated with fructose malabsorption:
http://www.medhelp.org/user_journals/show/21247?personal_page_id=494312

Low gastric acid (in atrophic gastritis) slows down peristalsis and some medications like antiacid drugs and painkillers do the same.