The sunlight (UV) was my thought as well, without enough sunlight to generate Vitamin D, calcium is not used properly - so it IS possible to get enough dietary Calcium - yet to have a deficiency because that calcium is not utilized correctly in the body. Perhaps the significant amount of cuttlebone eating is because they are deficient.I tend to agree. The shell looks thin.
If she is getting plenty of calcium there may be some other cause. Is your female very young, or just starting to lay eggs? Does she get natural sunlight?
Time will tell, be patient.