Have you tried the hole in the nappy thing? Ie: start with saying to her ok you'll put a nappy on her, tell her that "you can do it in your nappy, BUT you have to sit on the toilet to do it..." let her go in her nappy while sitting on the toilet. Do this for a few days and let her get the hang of it. it's about her being comfortable with going on the toilet and getting used to the surroundings, while giving her that familiar thing of her nappy.
Next, let her do the same but have a nappy with a hole cut in it in the right place, (ok, so, it has to be one prepared eariler, have a few on hand) so that the poos will actually fall into the toilet, put a bit of toilet paper in the toilet first as sometimes they get scared that it will splash them. again, its still the familiarity of the nappy, but getting her used to having it end up in the toilet, once she's got that downpacked it tends to just be the last move to help her realise that well, she's pooing, and it's going in the toilet anyway, so no need for the nappy cos WOW she's a big girl, etc etc.
just something that you could try. sometimes its just taking the child's approach to things and using a bit of imagination and trickery to turn it into the desired outcome that you want.