I'm hoping to get help w/ this issue as well as many others if/when we ever get a formal diagnosis for our son, who we are sure has AS. He's had a problem w/ holding in bowel movements since he was 1 year old (and NO, he was never abused and I hadn't even bought a potty yet, let alone tried to train him at that age.) He also started hiding his soiled underpants recently. We just made a new rule, that if I notice him squirming, butt cheek clenching, or any other of his weird movements that tell me he has to poop, then he HAS to go and sit on the toilet and try, no matter what he is involved in doing at the time. He often insists he doesn't have to go when it's obvious to everyone around him that he does. Btw, he's been on Miralax off and on for years for this problem. Holding in poop can cause some serious medical problems. Look up encopresis. If she's holding it in and only going when she absolutely can't hold it in anymore, she may actually NOT be able to feel it, and may actually be pooping around an impaction. This is something you really should discuss with her pediatrician, imo, it can get very serious.