Hello - I have not read the thread with the problem with your child and this may have been discussed before - but there is a condition called encopresis (I hope this is spelled correctly.) It is a medical condition where some children and adults do not have the proper nerve ending feelings in the end of their colons. These nerve endings make a person feel the urge to go. Their stool just sits there and becomes LARGE and very hard. When the colon gets too full, the body will simply push out the stool without the person being fully aware of it. The stools are large in size and are very very foul in odor.
I only know about this because I helped a lady in South Mississippi with her 4 year old son. He was potty trained, but would seem to "hold in" bowel movements, then he would soil himself with no apparent warning. His stools were very large and foul - it was no wonder he was scared to have a bowel movement! They hurt! Long story short - he got cleaned out with several enemas, he then had to be trained on a schedule to go poo. He takes a vegetable based stool softener one night and a senna type laxative the next night. This helps his stool stay softer and it helps his colon stay cleaned out so he can feel he urge to go. He only soils himself maybe once every 6 months or so now and it's been 2 years since he started treatment and training.
There is a website about it and I have it written down around here SOMWHERE - anyway, this may not be her problem. If it's not, this post might help some other folks. If you think this might be worth looking into, let me know and I'll dig out that website address. All the best to you.