How do I potty train a stubborn 2 1/2 yr old?

My daughter is two and a half and we are having trouble potty training her. She goes at school all the time just fine, but when we get home she refuses to go. She screams and cries when I put panties on her. She will hold it for over an hour, screaming and crying that she has to go. She won't go in any of the potties that we have at the house. She has gone pee and poop once in the toilet at home and we made such a big deal out of it; stickers, candy, etc, so I thoght she would keep going. But she refuss to go now and I don't know what else to do. It is so frustrating!