We had one mare that injured her leg 2 or 3 winters ago. She was sore & didn't eat well for awhile & lost some condition--kind of a poor doer that winter. Anyway, in late winter she had dandruff like that--her skin was just so dry & flaky/scaly. Since it was too cold yet to bath her, we'd just brush her, and as well we added BOSS to her diet. In just a couple of weeks the improvement was amazing--the dandruff went away, her skin softened up, and her coat got soft & shiny. Something like BOSS would be the first thing I'd try for your girl, because her dandruff & coat look very similar to what our mare was like.