Somethings Not Eggsactly Right...
Is your hen fully feathered because they do stop laying if they are having a moult. If she appears to be a bit bald underneath the wings, around the breast and belly, she's possibly moulting and the eggs will start to appear again once she begins to grow new feathers. Moulting takes a lot out of the hens and egg laying is usually the first thing to suffer as a result so you can help her get back into tip top condition by adding a little pinch of Poultry Spice to their layers meal or some chicken tonic in their drinking water to correct any mineral imbalance caused by them trying to grow new feathers.
They do stop laying occasionally so don't worry too much unless she is showing other signs of illness which is the most common cause for a pause in egg production. You can usually spot an unwell hen a mile off. They tuck their heads into their necks, hunch themselves up, puffing out all their feathers and droop their tails. They tend to stand around with their eyes closed, withdrawn from the other hens. They can also take themselves off into the Eglu and sit in the nest which often gives the impression that they are broody but they look sick and depressed and are quite different from a real broody. If she has persistent diarrhoea, isn't eating or drinking, that can also be a sign of illness. If she does show any of these signs, pop her down to the local vet for a check up because she could have an infection which can be cleared up with antibiotics. If she seems perfectly perky and is carrying on as normal but just not laying, you can usually put it down to dull weather not providing enough daylight to stimulate egg production.
Does she seem very thin? Can you feel a very sharp breast bone poking out. If she's underweight, she won't lay until she has enough body reserves to do so. Give a good layers mash or pellets to build her up as this should make up the largest part of their diet during the day because it contains all the necessary nutrients for good health and good egg production. They need plenty of clean drinking water as well to keep them well hydrated to lay. Hens that are too fat also don't lay so if she seems very plump and heavy, don't overfeed with corn or treats and stick to a proprietary layers mash or pellets instead. It's worth having a week's trial with no treats at all to see if this makes any difference. If you also ensure that they always have access to crushed oyster shell and grit at all times as this is necessary as a calcium supplement to help them produce good quality eggshells.
An infestation of internal parasitic worms can affect egg production and cause loose, watery droppings so it would be a good idea to give your hens a reliable worming treatment to make sure that they haven’t developed an infestation.
Infestations of skin parasites can cause a reduction in egg production as they suck the hen’s blood and can cause anaemia which weakens the bird and can also cause a loss of appetite in the bird. Dirty vent feathers, lots of scratching and dustbathing, hunched or withdrawn hens and soft shelled eggs are often indications that your hen has an infestation too. Mites can’t be seen easily with the naked eye but they leave the skin looking sore, red and featherless. Lice can be spotted quite easily. The hot spots where lice tend to hide are around the vent, under the wings, round the abdomen and chest and the neck area. Ruffle the feathers against the direction of growth and look for little scuttling creatures or tiny cream eggs stuck to the feather shafts. If you come across any, you can get louse/mite powders from various sources such as poultry feed suppliers/farm suppliers and some large petshops. Apply it to all your hens and repeat the treatment after a week to catch any eggs which might have hatched out. Depluming mites don't respond to some of the mite powders on the market so if there's no improvement, try one which has Pyrethrum or Permethrin in as these are very effective against this particular mite.
Red Mite don't live on the hens but live inside the hen house and move onto the hens during the night so if you check in all the corners, pull out roosting bars if you can, check around the roof for signs of infestation. They aren't particularly easy to spot as they are only about 1mm long and are grey before feeding and red after due to the blood that they suck from the hens and this blood sucking can lead to anaemia and lethargy. If you have a red mite infestation in your chicken coop, you may see tiny blood spots on the hens eggs and there may also be a greyish powder which can be seen around the ends of the perches. If you wipe the undersides of the perches with a clean white paper towel and find red streaks on it, this will show that there are red mite in the coop. Spreading Vaseline or nappy cream on the ends of the roosting bars and in the ledges where these bars sit can trap red mite too as they head for dark crevices during the day and any which do become stuck in the sticky cream can be wiped or washed off. To treat an infestation, you will need to remove everything from the coop which can be taken out and spray with a proprietary red mite treatment. Steam cleaners are also very effective for eradicating lice and mites from coops. Diatomaceous Earth is probably the best treatment to use on the birds if an infestation is discovered as it dessicates the mites.
Finally stress can lead to egg laying problems. Barking dogs, noisy children, loud machinery, birds of prey, vermin, bullying by other hens etc can also upset your chicken and cause egg laying to stop.
It’s also a good idea to check under bushes and behind garden sheds etc if they have been free ranging because it’s not uncommon to find a big clutch of eggs somewhere out of sight when you thought that your hens weren’t laying. We had one hen who used to like to lay her eggs in a big planter full of runner beans!