it certainly would not hurt to ask for Revolution and a skin scraping! I am currently going through something similar with my hedge. We have done the improved diet, mite treatment, use a humidifier, and spray her with humilac a couple times a week to soothe her skin (oils were not working for us on her food or on her, but humilac helped). She still loses anywhere from 1-10 quills nightly, and is starting to get sparse after two months of this. Hopefully someone else with more knowledge will be along soon!!!
It is so frustrating when you can't figure out how to help your little critters. The only other thing I could think is perhaps you could switch to fleece bedding? It seems like all the loose stuff really can be troublesome and cause extra dryness.
P.B./Pinto Bean/Peeberton/Peebs/Little Miss