S.W.
She doesn't know why she's doing it. And it is a normal thing for children who have been potty trained to regress. It's OK to let her wear diapers again for a short time, get over you being mad, and start over with the training.
My daughter was trained by 26 months. I started, slowly, when she was 14 months old. I knew with her personality that if I didn't start early it would become a power struggle. Don't make this into a power struggle with your daughter. She isn't doing this to make you mad. But, if it makes you mad, she may decide to keep doing it. At some ages, any attention is good attention. So take a deep breath...
(Yes, our kids can "piss us off" some times.)