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It is hard to say but in a young dog with 'patchy' hair loss mites will be high on the list. If there are less than five spots then it is localized and may clear on its own, if more than five spots appear then it is called generalized and medicine is used. Ask your veterinarian whether they would be willing to try Bravecto in this case. If she falls into an early weight bracket (ie she is 23 LBS) then they can give you the medication as she is unlikely to get to the next weight bracket (44LBs) before the Bravecto has cleared up the issue. Bravecto is a flea and tick medication that has an off-label use in demodex and sarcoptic mites.
Your veterinarian may want to do a skin scrape to confirm that it is mites prior to starting the medication.