You can do a mite test on her. (Gently!) Rub/pet her with a black t-shirt (or let her walk around/cuddle with it for a while on your lap) and then look if there's any flakes. If they're moving they she has mites. If they're not, then she has dry skin (if it's just a couple of flakes, I wouldn't worry about it).
Another to check for mites is to look at one of the quills. If there's a bulb on the end of it, then she's just quilling. If there's no bulb, then it's probably mites.
Again, it sounds to me as if it's just her quilling and she's handling it very well-- but it's never a bad idea to safe than sorry =)