Days are getting shorter already. Maybe she just doesn't have enough hours of light?
I'm not sure whether that affects new layers at the same degree as seasoned ones - seems plausible that a duck who is just getting the hang of laying eggs might be more susceptible to any of the triggers that make them stop.
Has your routine changed at all? Since the start of the school year, we've started putting the ducks to bed early so that we can get the kids in bed, and many mornings we're rushed enough that I don't get to the ducks until the bus has come. I'm not sure whether there's enough light in the duck house to count toward "hours of daylight".
Is it possible that a snake or something has been stealing the eggs?