P.D.
Does it seem like a power struggle issue? If so, you could put her back in diapers and tell her when she's ready to use the potty and be a big girl, she can go back to underwear. Then back off and wait. Kind of a pain, but at least you won't be cleaning up her accidents, and it gives her back control of 'when'. It probably won't take long if this is what the problem is. If it is something else, clearly this approach won't help. You still may want to rule out the urinary tract infection possibility. It can't hurt. I hope you get this sorted out soon! P.S. Night training may take significantly longer, no matter what is causing this.