K.C.
I'm sorry you're having a rough time but hang in there. I never pressed the issue with my daughter who was 2 and 1/2 when she showed interest in potty training. I too allowed her to pick out her panties, however we would throw them away if she messed in them and that seemed to do the trick. (sounds mean, I know.) Needless to say, she only messed in them for one week and from then on we've had no problems. I hope this is helpful.
P.S.
When throwing her underwear away we made it very sentimental which I believe was the trick. It was sad for both of us.