You can see mites and lice so all she needs to do is look her duckling over real good or go and run her hand under and through their bedding [watch out for poop]and most likely if she has mites they will crawl up on to her hand and lice congregate around the shaft of the feathers around the vent and under the wings close to the body. Mites are tiny like tiny specks of pepper, lice look like grains of rice. Pics on line.This is what has me concerned that this is not just molting. My 2 cents