Sounds to me to be an allergic type reaction. The pattern you are describing is commonly referred to as a "miliary" pattern and is often described as "miliary dermatitis". I am surprised to hear that she isn't itchy, you may try and lightly scratch her back and judge her reaction. If she twitches and tries to scratch with her legs or turns her head and tries to chew, then you may be under estimating the itchiness of her skin. If not, then I am glad because itchy skin is never any fun. I will tell you that any vet you see will suspect a flea allergy until proven otherwise. It is still the most common allergic reaction seen in dogs and cats and the pattern you are describing still fits with this particular diagnosis. If you are using a monthly flea control product for your dog and any other dogs or cats that you own, then you should have very little concern that this skin problem will be a chronic problem. Your dog could certainly have been bitten by fleas in the environment it was in while you were away and the fact that you don't see them now does not disregard the allergic reaction that may have begun.
My advice, if the itch is mild or not at all, you can use over the counter Benedryl (Diphenhydramine HCl) at 1 mg per pound of dog. So a 25 lb dog gets a 25 mg capsule or tablet and a 50 lb dog gets 50 mg. It is very safe and don't worry that your dog would get a higher dose then you might take. Dog's tolerate the medication much better than we do and require higher amounts to work. You can give this medication 2 to 3 times daily for mild itch or mild skin reactions. A hypoallergenic shampoo can help remove any residue from any shampoo that could also be causing the reaction (you mentioned a grooming recently). If the sores are bad enough, an oral antibiotic may be needed which would require a vet's visit.
Other skin diseases such as ringworm or mange would seem less likely given the pattern but not impossible.
Thus, for mild itch and scabs that aren't spreading = flea control, oral Benedryl, hypoallergenic shampoo and observation.
More intense itch with spreading sores = Benedryl tonight, vet check up when able for skin check, microscopic exam, and possible antibiotics.
Hope this helps,
SoCalPetDoc
Dogs that are allergic to fleas are always allergic to them. We use flea control products to prevent infestations in and around the home where our pets spend most of their time, thus reducing the chance for flea exposure. If you have been using flea control regularly, then the chance that you will have a flea problem is small but that doesn't mean your dog wasn't exposed. Get back on the monthly flea control, use it all year round, and see if the skin responds to the antihistamine and time. If it gets worse, the vet visit is always available. Once the dog is out of the flea environment the reaction will only worsen if the dogs itch is not controlled. Control the itch, get the flea out of the equation, and the skin will heal.
Cheers,
Dog Veterinarian
7yrs in family practice, internal medicine, surgery, and geriatrics for both dogs and cats