3 year old refuses to use the potty

I am out of ideas to potty train my 3 year old daughter. I have tried a sticker chart, M&Ms and just putting her in undies. She currently refuses to sit on the toliet. If I put her in undies, she will take them off and find a pull-up to put on. There were days she would go at least 6 times on the potty, now I can't even get her to go once.

She went #2 on the potty only once and it was by accident, I am pretty sure.

Any ideas would be most appreciated. Luckily, preschool doesn't require the kids to be potty trained. She will be starting in August and I am hoping that seeing the other kids going to the bathroom will help influence her.

Thank you,
Kim