B.B.
What always worked with us was the "potty first" rule. Kids at that age just do not want to take the time to go potty. There's nothing fun about it, and it takes time out from doing fun stuff to have to do it.
Any time she wants to change her activity (go from coloring to watching TV) or wants a drink of water...anything that's different from what she was doing, "POTTY FIRST. You can do whatever you want....but potty first." (and then keep track and if she hasn't gone potty in about 15-30 minutes, and wants to change activity again - potty first.)
As she got a little older, if she "relapsed", we'd set the timer for 30 minutes, and had her go potty every 30 minutes. Once she groaned, "I know...go potty." and we told her if she would do it herself like she knows how, we wouldn't have to do that. Soon enough she got the idea.
Good luck!