No sightings of her today? Hope she shows up tomorrow. Normally if they are making a hidden nest they will keep laying eggs in it but come back to the coop and act normal until they decide to set, which is when they would disappear except for once a day or so when they will come out to eat and drink. So they really should only be gone for 23-24 days or so (21 days to brood and another day or two)... but even then you may see her during the day occasionally. If you catch her and lock her up for a few minutes, you can usually follow them right back to the nest. I have had some of them hide nests quite a bit away from their coop, others really close, so that just seems to depend on the hen.