No Roos. Raised them from 2 day old chicks. 2 leghorns 2 buff orps 2 RIR. I have a small coop and they free range from dawn to dusk. They used to roost in a tree at night. I let them because it's been average temp 100 here. But lost one RIR to a possum last week so it's back in the coop at night. I feed layer feed. Access to oyster shell. Cool water mister during day that's around a shade tree. Fresh water I add ice to during day. Treats are mealworms, watermelon, grapes and 1 cup scratch in the morning.
I'd bet there's your answer...she could very well be laying out in the range area somewhere.
Sounds like it's too hot to lock them up in the coop but:
Free range birds sometimes need to be 'trained'(or re-trained) to lay in the coop nests, especially new layers. Leaving them locked in the coop for 3-4 days can help 'home' them to lay in the coop nests. Fake eggs/golf balls in the nests can help 'show' them were to lay. They can be confined to coop 24/7 for a few days to a week, or confine them at least until mid to late afternoon. You help them create a new habit and they will usually stick with it. ..at least for a good while, then repeat as necessary.
The heat can also have an affect, all that water they drink is being released to shed heat from the body, so not enough left for making eggs.
I give my birds a small dose of electrolytes/vitamins(save a chick) once in awhile in the hot weather, gives them a boost.
They may also be a bit short on the protein levels:
I like to feed a flock raiser/grower/finisher 20% protein crumble to all ages and genders, as non-layers(chicks, males and molting birds) do not need the extra calcium that is in layer feed and chicks and molters can use the extra protein. Makes life much simpler to store and distribute one type of chow that everyone can eat. I do grind up the crumbles (in the blender) for the chicks for the first week or so.
The higher protein crumble also offsets the 8% protein scratch grains and other kitchen/garden scraps I like to offer. I adjust the amounts of other feeds to get the protein levels desired with varying situations.
Calcium should be available at all times for the layers, I use oyster shell mixed with rinsed, dried, crushed chicken egg shells in a separate container.
Animal protein (mealworms, a little cheese - beware the salt content, meat scraps) is provided during molting and if I see any feather eating.
