What type of heating do you use and do you have a thermometer right in her cage? Is there enough lighting? Has something changed recently that might be allowing a draft on her? Is she at floor level, or under a window.
Sometimes repeated hibernation attempts when heating/lighting/etc is all okay, is a sign of an impending illness. As they age, they often require more heat. Usually this happens closer to 3 or 4, but can happen as young as a year.
What is the temperature that she is hibernating at?