K., I'm sure this is frustrating for you. Just when you thought potty training was over, you are starting again. As many others have said, try to keep your frustration in check. Kids do not set out each day to see what they can do to make life more difficult for their parents, unless there are some serious issues at hand, of course. It sounds like your daughter just may need some reminding again. Kids forget. And, I doubt she really wants to go in her 'big girl' panties. So, make sure you let her know that you understand that it was an accident and empathize with her by saying something like "oh, I'm so sorry, being wet must not feel very good". Encourage her to help you clean up, get new clothes, etc., but without shaming her. The shaming does damage well beyond the moment of the accident. Children want to please, and sometimes need our encouragement to remember what it is that they are supposed to do. Another tip that I have, is bring the potty chair out from the bathroom and into the living room (or whatever room you spend the most time in). It will help you remember to remind her and it will also keep it top of mind for her. There is nothing wrong with 'encouraging' your children to do something with an incentive. At this age, it is how they learn what is the expected behavior and remember it the next time. After a while the incentives aren't necessary - when they've learned the skill or task. But, at first, giving her an extra story at bedtime, or a trip to the park, or an M&M, gives her the extra reminder that the potty is so much more rewarding than having to change clothes and feel wet. Also, she may be on the cusp of an emotional or physical development leap. And, when these things happen, sometimes kids spend so much of their energy focusing on developing that skill, that some of the things they already learned will slack off.
Good luck!! It's hard to be patient, but keep reminding yourself that it is temporary and she's not doing it to displease you.
L.