She may be sick. Watch for any symptoms of illness.
Google egg bound. Sometimes eggs can get stuck in hens and cause problems. That's something you'll want to identify and fix right away.
The amount of daylight she's getting could also be a factor. If she's getting less light every day, hens will stop laying.
If she's not getting enough nutrition she might also stop laying. If her eggs up until now have been thin-shelled, she could be low on calcium. Make sure she's getting a well-balanced diet and enough food, and give her a calcium supplement-crushed up eggshells work well for this.
There may be other reasons why she's not laying and it could be normal, just keep a close eye on her and see if there is anything else to be concerned about.