Hyperthyroidism was the first thing that popped to mind; however, that's one of many other symptoms. It could very well be seasonal allergies, or it could also be dry skin with the cold, dry weather moving in (unless that isn't the case in your neck of the woods!). I wouldn't think 'food allergies' since she's been on this food before with no incident. But... since you temporarily had her on a different food, it COULD POSSIBLY be a reaction to that food you had her on.

If it were my pet, I would bring her in for a vet checkup, because as you see here, it can range from "no biggie" to "biggie".