Oddest title I've typed so far 
DD is 5, in reception at school.
When she started school she was dry, no problems with accidents etc - though we did have some real problems toilet training her as MIL took it upon herself to train her at 18 months, well before she was ready, and wouldn't stop regardless of how often we asked her to. MIL provided free childcare for us so it was a bit of a rock and a hard place situation 
Anyway by the time she started school we thought things were sorted. She had one or two accidents before easter, coinciding with doing something new and interesting. Understandable.
Since the easter holidays she has had accidents almost every day. Ranging from not quite getting to the loo on time, to full on wee dripping down her legs. It happens at home and at school. When it happens she doesn't tell anyone and eventually her skin gets sore. She also (obviously) smells 
We have asked her why it happens and she says she is 'too busy' or 'she forgot to go'.
She doesn't have a UTI and her school assure us there are no problems that they can see in the classroom.
We have tried reward charts, talking to her, ignoring it and getting her to sort herself out (so it takes longer to deal with than it would have done to simply go to the loo). We, and the school remind her to go regularly etc etc. I just don't know what to do. She is otherwise her normal, happy self.
The only change I can think of is that it coincided with her becoming dry at night - and she wakes up at night, gets out of bed and goes to the loo.
I feel awful, as I am started to get frustrated with her, and cross and then she gets upset and promises she will try harder. Then she doesn't. I am also really worried that eventually the children at school will begin to notice and tease her.
I know AIBU isn't necessarily the place for this but I am hoping with the high traffic someone will have been through similar and have some idea's that I haven't thought of on how to help DD.