Ugh.....Potty Training

I can't do it. Or rather, she can't do it. Pee on the toilet that is. She sits on the toilet for about 15 minutes, whining the whole time, then after she's off the toilet, she pees her pants. Ugh - it's so frustrating! Yesterday I had to clean up 3 "accidents." What am I supposed to do? Any advice out there? She's 2 1/2 and should be ready for this - all the indicators are there, except for her willingness. She's been offered rewards, punishments, cajoling, etc......