Potty training....HELP

My daughter will be 3 the end is September. We tried the 3 day potty training and it unfortunately did not work. She lets me know when she is wet and completely understand pee pee on the potty....she just will NOT sit.
I don't want to pun it and turn her off from it all together but would like her trained by September. She will be starting preschool at St. Gregory's (3 mornings a week). They said she can wear pull ups but if she poops someone will have to come and change her. Fortunately, she usually dies that at night and she actually doesn't pee to often while wearing a pull up.
Any advice is appreciated!

Potty training....HELP

We have 3 girls and the older two were both fully potty trained by the time they were 2. And we are training the 14 month old now. There is no pressure. When i go to the bathroom I take her. While at home we let her go with out a pamper (she has some type of leggings on) We ask if she has to make. If her response is yes we take her to and bathroom and sit with her while on the potty. Even if she does not go we get excited because she sat on the potty. We did this with the older two also. As she gets older we (my husband) and I would/will take the her. Even when we get up at night to use the bathroom we woke them up and sat them on the potty. I found that just having a consist routine with no pressure worked best. Good Luck
Oh yea, we also traveled with potty in the car.