occasionally a hen will get a "hiccup" wich pretty much is she got bothered and it messed up her egg cycle this normally clears up within a day and she's back on her regular cycle
Did she get a bit of a scare recently?
Did she stop laying for a few days and then start again? if so she may have just stopped and started up again and need to "get back in the groove"
did you add a knew member to the flock?
has there been any squabbles that have been a little bigger then a peck away from the feeder?