If you are worried by this do discuss it with your Doc. Some children do digress a bit,if they get potty trained early it can happen and it will pass, dont make an issue of it as it will make her anxious, be matter of fact ',and say"accidents do happen'It could be she doesnt make it there on time just let her change and dont concern the more you make of it the more it will become.
It could be a weak bladder, I would discuss it with her doctor.