From what I know, doing a poo in the toilet can come a fair while after wees. The worry could be constipating her a bit so you are doing the right thing in not making a fuss. Can you try getting her to tell you when she needs to do one and get a pull up nappy on her? My SIL had the same issue and that was her trick. It just took the stress away from her DD as she felt it was ok to poo in a nappy but not in her pants, iykwim?