Ahh, OK so she's now approx 18 months...might be molting?
Could have been the heat... then a molt.......or she could be laying out in the range area
Might lock her in the coop for a few days:
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 2-3 days can help 'home' them to lay in the coop nests. 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.
Or could be shortening days too:
The not laying could be because of lack of daylight. Sometimes first year layers will lay all winter without supplemental lighting, sometimes they won't.
Older layers need 14-16 hours of light to lay regularly thru winter. Last winter I used a 40 watt incandescent light(this year I am using a CFL) that comes on early in the morning to provide 14-15 hours of light and they go to roost with the natural sundown. Last year I started the lighting increase a bit late(mid October), the light should be increased slowly, and the pullets didn't start laying until late December. Here's
pretty good article on supplemental lighting. Some folks think that using lighting shortens the years a hen will lay, I don't agree with that theory but I also plan to cull my older hens for soup at about 3 years old.
