Aren't we all? having our feather friends we are all there at one point or another, when it's not our turn we are here to support others that the chickens are just making us scratch our heads about lol.
more likely something interested her out there and she didn't have time to make it back to the box.
But I would watch so it doesn't become a habit, if she's repeatedly doing, it I would do a search or an invader where the laying boxes are and the room they are housed in or bullying at the...
did they just come off of a molt? Sometimes they will before or after molt as feather production takes so much out of them. calcium in liquid form shouldn't be added to water but given directly at the tip of the beak.