My 3 almost 4 year old niece AND my friend's daughter who is the same age both took FOREVER to potty train. It was getting very frustrating and it didn't seem to matter what they did there were constant accidents for months and months. They both have strong willed personalities, perhaps that is a factor? My niece had an issue with holding in her poop and that caused some real set backs too. But for both of them they just recently were finally fully potty trained, all that they did was keep consistently taking them to the potty and eventually it just clicked.

Sorry I don't have much advice to offer, except that it took time and endless patience. But if the girl is pooping herself she would definitely be in a pull up in my house. What an awful mess to clean up!