We had the same problem with DS1, and as everyone else said, we just gave him time and a bit of encouragement, but not pushy, as this made it worse. Might be worth getting her to sit on the loo but with the nappy on when she needs a poo. then after a while try and talk to her about taking it off. I've heard this can work although we didn't try it. Goof luck! Hope she gets the hang of it soon but defiantly don't stress about it, she'll get used to it in her own time.