C.W.
This is totally normal. We are trying to finish the training with my son, and he is so used to pooping standing up that it is very hard for him to do it sitting. With my daughter, she had bonded with her poop (also very common) and viewed it as a part of her and couldn't bear to part with it. We finally told her that the poop was going to a party and she had to let it go to the party and it would come back to see her next time she went. Silly, yes, but she happily sent it to the party after that. My ped warned me that kids start to withhold when they go through the process. She recommended sneaking fiber in whenever you can so they can't withhold it. I give my son fig newtons, pears, raisons and other high fiber things to help him a long. Give her some time, she will eventually get it.