My eldest son did this. to be honest I just let him poo in a nappy.. when I relaxed about it he went back to regular poos and one day he did a poo on the toilet and he was fine. he was 2.5 when he TT and was around 3.5 before we threw awa the nappies in the day time all together,,

sometimes it is easier to just let her poo in her nappy but get her to tip it into the toilet and flush it. And tell her it is good she is trying but wees go in the toilet not in her nappy. Eventually she will pooo on the toilet i promise