I would persist, maybe when she asks for a nappy put it on her, but then put her on the loo. Maybe then she will get the idea a bit more? Then maybe in a while you could take the nappy off midway through so it goes in the loo? Maybe that will get her to make the connection some more.

But honestly DD1 was awesome to tt, DD2 was a nightmare, and it resulted in me making a massive deal with her.. yep I bribed her, and I obviously wasnt thinking at the time and was desperate.