have u sat her down and asked if anything is wrong, has she alredy started school or will she start in september, maybe this could be playing on her mind. alot of people say they wet themselves when they are worried about something. it may be just that she is being a bit lazy but at the same time there maybe something going on in her head that she isnt telling. i would try having a bit of time just the two of her, reassuring her that she can tell u anything and that u wont be cross. i knew a child that wet himself and it turned out he was being bullied.
maybe it is just a funny stage sge is going through, hope u get to the bottom of the problem good luck x