Look at her diet. Is she eating more junk and fatty foods than usual? Urination is one of the ways our bodies get rid of waste. If she is eating more nuggets and fries than usuall, I would back off of the junk food for a while and see if it helps! I know especially during the summer us Mommies are running constantly and need that quick meal. If that doesn't work, then I would threaten her with diapers again.
OK, I read your reply post and that changes a lot! She is going through A LOT of changes right now, I bet it is the stress of everything. Just remind her when she does have an accident that she is a big girl now and she needs to use the big girl potty. If she goes a whole week without an accident, she gets a new pair of panties! (let her choose of course!)