Hi A.,
It sounds like your daughter is like mine- smart and stubborn. At this age they do not have much control over things in their life- we tell them when to eat, what to eat, where to go.... Anyway, try giving her some more control in her life. Does she dress herself and choose her own clothes? My daughter does now and that has helped us in so many areas- sometimes she chooses inappropriate things- a skirt in the snow, but she is learning natural consequences- she gets cold.
Anyway, I try to give her choices when I can- Would you like your eggs scrambled or fried today? So she feels she has some control.
So back to the potty- My daughter will still hold it for hours and then at the last minute run to the bathroom. She usually makes it, but when she does not I try not to say anything. When she comes to me wet I say, "hmmm, I guess you should go find some dry pants." Or, "It looks like you have a problem. I wonder how we can solve it?"
When I see her holding herself I ask if she needs to use the potty. When she says no, I say, "I know you will go when you are ready." and that again gicves her control.
Good luck- I know it is really frustrating as a perent. :) S.