C.T.
Hi S. - there is hope in this situation. I am right there with her right now and am finally seeing some results. Do some background research on pediatric incontinence and you'll get a lot of hits on pediatric urologists.
My son is being treated by a urology clinic here in town that focuses on elimination concerns. The first thing they wanted to do is have an abdominal x-ray performed ( I did web search and this is not unusual). What the x-ray showed clearly is that his bowel was very full of soft stool and some places of very hard stool. (Sorry, TMI) What they explained to me was that even though he was regular, his bowels arent effectively clearing out the hard stuff, it's backing up the whole system and it's messing with the nerve signals we all receive to know we have to go to the bathroom. She said physically, it's just difficult to eliminate from a sitting position this way (aka the potty) because there is a lot of pressure being applied on the pelvic floor due to all of that stool.
Under the doctors supervision, he was put on an aggressive laxative regimen for a couple of days to clean out the hard stool and then a maintenance regimen to keep things soft and moving like they should. We're about a week into it and so far he hasnt pooped on the potty but the doc said that's okay. Once we're into the maintenance this week and we have dosages/timing etc. that is working for him, we'll be able to sit on the potty and he will be able to go.
My halleluja moment this morning was when he woke up dry and used the potty. It's working just like they promised. The followup from now on is going to be a reward system for new good behaviors (different from rewarding stopping a behavior). She said to only reward the behaviors we want to keep. I liked that. She said to go to the dollar store with my son and have him pick out some of those individually-wrapped toys. Those go on a visible shelf in the bathroom. We're supposed to talk about what a neat toy he gets to pick out after he goes poop in the potty. She said put the emphasis on the special toy, activity, time with grandma, etc. rather than on them using the potty. The toy is in the bathroom and they know they can have it when they poop - no nagging needed. I like that too. The last thing she recommend and actually gave me a letter to give to preschool was that he should be drinking lots and lots of water (50% of body weight in oz. water) and that he should be going pee every 90 minutes. There is even a little watch they wear that will vibrate or play a little song when it's time to go so you dont have to take them or remind them. There are other charts and rewards that will be coming - the basics are to get their bodies working properly and allow them to learn to control their elimination.
I hope my experience helps you with your grand-daughter. Please also know that I strongly recommend to not pursue the laxative approach unless she is under a doctors care.