C.H.
I went through the exact same thing with my daughter. My husband and I were seriously giving up becuase we had tried everything. What finally worked was when the time came and we would see her sneak around the corner to go poop, we would go get her (even if she was in the middle of it) and put her on the potty and hope that she could finish, or at least get a little bit in there. When she did we would praise her like you don't even know. I know that you might have heard this before but we would seriously praise her and show her what was in there and tell her it was going to go home with all the rest..But the praising is what worked for us, and believe me it wasn't like it was a go the first time, it took a few times but then she realized how much she like to be praised..She has been wonderful ever since, she will be 5 in July and she has never had an accident..Hope it works for you.
C.