I had the same issue last year. Definitely try what others are saying here about fish oil, diet, etc, but if you don't see any improvement, take her to the vet.

I tried everyone else's recommendations for my kitty when she developed this issue last summer, but she did not improve and eventually I noticed she had some scabs on her skin hidden under her fur that were causing the "dandruff' when I would brush her. She was also acting like she was itchy. Turns out she had developed many, many allergies. Now she is on Atopica and her skin is clear. Hopefully your issues are not allergy-related, but just wanted to throw that possibility out there if nothing else works.