J.L.
Has there been a change in routine? I would not resort to putting a diaper/pullups back on her as this creates a back-up plan. Not that your child is lazy but let's face it if they are tired and have a diaper on then why not use it...Plus these days with the padding they don't feel wet LOL! I would have her actively help you clean up. Make sure she is not drinking at night after a certain time and have her go potty before bed. 3 is a little young for accidents not to happen. Also, create a reward system for her staying dry at night.