No Interest in "Big Girl" Underwear

I am making every attempt to potty train Gabriella. Gabriella has (unsuccessfully) worn underwear in the past, but, of course, I keep trying. I took out her new Dora underwear and showed them to her. She yelled, "Aah" and jumped back as if she were afraid! We put them on and she kept admiring herself in them. I kept reminding her that if she had to go potty she had to tell me so that we could go on the potty and so she wouldn't wet her new "big girl" underwear. After questioning her many times, she said she had to go. I put her on the potty, but there was no output. Moments after she was off the potty, her new Dora underwear were wet. The diaper is back on and it is no big deal to her! I am thinking that when she is in the first grade I will have to volunteer with her class so that I can change her diaper!