I don't have much advice because 4.5 y old DS is in a pull up at night. He physically can't hold it.
You could try waking her in the middle of the night and taking her t the bathroom. This always scares me, though, because I don't want him to start partying in the middle of the night.
What is her liquid intake in the evening? 3 is still pretty young, even for staying dry overnight when she is PTed. My DS went through phases where he wet himself at night and I just limited his liquids and fruit in the evening and that helped. I also would take him potty in the middle of the night once.
I'd check a UTI, but it could just be normal. My son went through something similar. We just put him in pullups and put a pad on the mattress. The pedi said it was just normal body development and he'd grow out of it. He did grow out of it.