Is her fur dry too? Or is it just her skin? Is she scratching a lot, like she's itchy, or does she just have dandruff?
If she's scratching..it's probably an allergy. If she's not scratching, and her fur is dry too, she might just need more vitamins and minerals, or fat even, in her diet. Royal Canin makes a skincare formula.. it used to be Skin and Hair or some such, but I think it's Skincare 30 or something now. I think they're about the same price as what you're paying now. Salmon Oil contains the omega-3's and may contain omega-6 but I'm not sure. You might also try just adding a supplement to her existing diet.. I know there are some others out there, but we use WildTrax, and it can be found at www.jefferspet.com
If you think it might be an allergy.. it might be the grains or additives in your dry. (It may also be the chicken as someone else suggested). One way to rule that out is to look for a raw based dry, or try feeding wet that has no grains added...from what I understand it's usually the "grains" that is the culprit, and somewhat more specifically, corn.
In either case, it's probably easiest to try a supplement of some sort if it's not definitely allergies.