H.H.
I read the other responses and I just have to say: PLEASE don't PUNISH her for not going! That's terrible (yes, judgemental of me, but it is) and studies have shown how truly traumatizing it is for kids to be punished in this area.
How old is she? That may be a part of it. Kids need to be emotionally and developmentally ready, not just physically ready. This is one of the few areas in their young little lives that they can control, and they certainly push that!
Consistency is key. Kindly remind her and take her every 20 minutes or so until she has learned. But punishing her is not going to help her to learn. It's only going to associate potty time with punishment.