This is the time they are brumating. I would first ask , does she seem okay other than not eating?
Is she trying to sleep, (not basking as much?) If she appears okay and is not losing any weight, but seems tierd I would let her brumate. Even turning up heat sometimes does not keep them from sleeping if they really want to.
Its up to you if you want to bruamte them. This stimulates breeding in the spring. 
If you do want to, you have to not feed them for about 7 days, so their tummies are empty of food. Then about 10 days later turn of heat, and then a week or so later turn off the UV light.
You can give them a months sleep and see how they do. But if you decide to do this, remember to give them water atleast once or twice a week with dropper. They can dehydrate if you don't.
I always check them, to make sure they are not losing weight while sleep also. IF you notice they are STOP.
Let us know what you decide and how she is.
Just make sure she looks okay and has not lost weight from not eating, before you consider brumating okay ! 
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Eve / PHEve