'Tis the season. During fall into winter, the days are getting much shorter and many hens stop laying. It's a normal part of chicken life. Hens use the Winter season to rejuvenate and recover from a spring and summer of egg laying. If you want her to continue laying, you'll need to add supplemental lighting so she gets 14 hours of light. Keep in mind that forcing her to lay throughout winter may shorten her years of laying and her life.