Re: Regression...sort of?
I am having the exact same problem right now with one of my 2.5 year old twins. She is definitely doing this on purpose and driving me bonkers! She had been completely potty trained for a few months and then started peeing in her pants when she was in a time out for something unrelated. I definitely blew it because I overreacted and now I think it's a game for her. Other than trying to remain calm, what I'm trying now is: bought her new, highly desirable underwear; offer her a special treat (a jelly bracelet) if she has no accidents the entire day, giving stickers again for each pee. This has worked for the past few days so I have my fingers crossed. I think the end of the day special treat seems to be the most effective.
Good luck and keep us posted what works for you! Definitely don't put her back in diapers.