The sign of pus means the wound is already infected. I've never had an infected wound in our chickens but I'd probably do what I do to my own wounds. I know you say you don't have a place for her inside, but an infection left untreated is dangerous, and so is being outside in the cold. Do you...
We had a hen with a vicious, deep gash in her side before (exposed very deep, but no blood, could see to the muscle). We applied blue kote once but that was the most she let us do. The wound healed within a few weeks. I find with wounds, chickens are extremely hardy. Just watch for any sign of...