T.D.
Can you add a little more information? Is she still wearing training pants or underwear? Does she have accidents or is she actually holding it in all day?
I also have a strong-willed daughter and this is what worked for us:
If she isn't wearing underwear, try putting her in those and stop using the training pants. My daughter hates getting wet.
If she is able to hold it in all day, I would be concerned that she is not getting enough water to drink. Maybe offer her more water. My daughter would have "askidents" at least once a day and would still refuse to "try" if she didn't have to go right when I asked her to.
You can also try getting a potty watch. Basically a timer that you set to go off at certain intervals. When it is time to "go", it blinks and plays music. My kids loved going when it was time and made a big deal out of showing off their "new potty watches" to everyone. It takes you out of the equation so it is no longer a battle of wills to go. They are $10 at pottytimeinc.com. I always had my kids go potty first thing when they woke up and then they "got" to put their potty watch on. Then all I did was get really excited when the potty watch went off ("it's time to go potty! YEAH! Hurry up! Get there before the song stops!", etc.) and they did the rest.