M.M.
I agree with Dana K. -- tell her it's time to go, rather than asking. My son does the same thing. I make peeing in the toilet a condition for just about everything -- let's build something with blocks, but you need to go potty first. Let's go for a walk, but you need to go potty first, etc. We also STILL use rewards (packs of fruit snacks) for those stubborn moments when he just keeps refusing. You could do a star chart with a small prize for 10 stars collected (Dollar Store item does it for my son!). Good luck!