What about other vitamin supplements? If she doesn't have a broad diet that could cause it maybe? Another could just be age. 12 years is getting old for a bearded dragon, I haven't heard of any healthy ones living past 16 with 11-13 years old as the standard age.

Considering age, I would look further into various vitamins. Then I would work on getting as close to perfect weekly intake of each type of vitamin that is essential as I possibly could.

Best of luck with her.