Have a No More Diapers Party. Set a date for being in undies at least 3 weeks from now. Talk it up, circle it on the calendar, count it down, get excited and make it as exciting as a birthday.
On the date get a small cake and sing "No more diapers" (pick a tune, any tune that is happy) and eat cake. I prefer to do it either first thing in the morning or right before bed the day before. Then after you eat the cake, she can only have a diaper on if she is in bed. Otherwise, sorry, we sang the song and ate the cake, no going back, the rule is you have to use the potty.
She may immediately be potty trained, or she may have a week of accidents. But the key is not to go back and to remind her that this is a new rule and just like not running into the street it has to be followed or there are consequences. At first those consequences should be just a reminder, but into the second week they may become more strict if you want. If she asks for a diaper tell her, sorry, we had the party, ate the cake, sang the song, there is no going back.