My mojave female did the same thing at roughly the 500g mark with no changes to husbandry/location/activity etc. After October rolled around, she decided she wasn't so much into the feeding thing. She went from weekly F/T rats in the 50-60g range to the occasional (every 3-5 weeks) live rat pup or small juvie rat. She's maintaining her weight, so I'm not too concerned. From what I understand, it's not unusual in the winter for them to go off feed. Keep offering now and then, and she'll let you know when she's ready to go back to more regular feeds.