We had a problem with a hen that the roo had mated. She was shaking the flour off like you described. I mixed in a bit of sugar so that the dry goods mix was 1/4 sugar and 3/4 flour. Then I misted the back of her neck and I dipped her entire head in the bowl of flour sugar mix. It got all over her, she looked funny and she shook so do it outside. But that sugar and the misting seemed to retain enough flour that it still "scabbed" up after the shaking was done.
Currently my layers get let out by an auto chicken door into a run. Then once I feel like it, I let them free range. It works well for us but the birds to pace the fence line sometimes trying to encourage me to get myself out there in the cold.
Thanks - she seems to have stopped bleeding now, so I will keep her isolated for the time being and keep an eye on her and try that later if needed. I'm laughing over dipping a chicken head in a bowl of flour/sugar. Her best friend is out there crying for her but every time we go to open the run for her she runs - she's the most skittish of the flock.