The best way to get a BP to eat is starve it. For a male, you may as well and save yourself some feeding costs.

The second best way to get a female BP to eat is breed her. I've heard of people who had female bp's who would only eat mice or only eat gerbils, trying all the other methods out there. However, after the female laid, they were able to feed it a rat no problem and keep it on rats since.

Now, if she stops feeding at this time every year, there's really no reason to worry. You say your temps are right, but her cycle might be going according to how many hours of light she is getting, or just even from when she was originally born.

Either way, as you said, she's not losing weight. If you don't plan to breed her, I'd starve her for a few months.

I personally believe one of the reasons bp's refuse food is that they know they can have it anytime they want, being fed on a regular routine, so they feel they can pick and choose when they want to eat, being "spoiled" if you will. This is not how it is in the wild, and they should not be afforded that luxury. As I posted in a thread a few months ago, varied feeding results in greater longevity. Most people tend to continue their bp's food even when they're not eating. Assuming bp's are intelligent enough, that just reinforces to them that they can eat whenever they want so there's no sense of urgency to take advantage of the food. If your BP's not eating, I would just not offer any food at all for several weeks.

I would also start to cycle my bp's... even if you don't plan to breed them anytime soon, you will at least have some control over their fasting period and then you will know for certain that they're not eating due to seasonal reasons rather than some health problems. It will also make it that much easier in case you ever do decide to breed.