I had so many setbacks on potty training my daughter that I can't even count them all. I did have to back up to using diapers a couple of times because I really didn't want to turn potty training into the control game it was becoming.
Finally, at three, we decided to take serious action. First, we got her to agree to stop using pull-ups. Then I had to deal with a lot of accidents.
And this is what worked in the end. We let her pick a BIG reward that she really wanted (Painting her room pick). Then, we got four sticker charts and pasted them up on the fridge. When she filled up each chart, she got a smaller reward, and when she filled up all four, she got her room painted pink.
I purposely broadened the rewards chart from JUST the potty, because I didn't want to make it too big of a deal. She got stickers for going pee pee on the potty, going poo poo on the potty, an extra one for going without me asking her, for asking for things in a happy voice (instead of whining), asking to be excused from the table when she was finished eating, sharing toys with her sister, or doing things the first time I asked.
In three 1/2 weeks, she had filled up all the charts. She was back on the potty every time, she asks to be excused at the end of every meal (so we can wash her hands before touching things) -- but we're still working on whining and listening :).
And she loves her pink room.