J.B.
Depending on what she has eaten or drank and how long it's been, determines whether you should make her go potty. If you're leaving the house, it's a good idea to make her go potty even if she says no.
Stay persistance, give rewards for going potty and things will fall in place with time. At three, I put my little boy in regular underwear, we had a few accidents, don't criticize the accidents, just tell her "now the time you need to go potty... tell mommy"
Good Luck