I agree with what the others said.

What also worked with the kids I have nannied for is giving them a stamp or sticker as a reward. This always worked well

Good Luck with it all. And just remember not to force the issue. It will happen when she is ready

Actually that reminds me. The little girl DH and I have babysat since she was 1 (she is now 6), well her mother never forced the issue of toilet training. She had just turned three and was still in nappies and one day said:" Mummy I don't want to wear nappies anymore!" From that day on she didn't wear nappies day or night, and just like that was toilet trained =D>