Oh no, I agree that her wound is more serious than I thought. You may want to get some plain neosporin (or vaseline) ointment and gauze 4x4, and apply the ointment in a gob to the gauze, and press it onto the wound to seal it. That can seal the wound for you to be able to secure that to her back with something stretchy such as panty hose or similar that can go around her. Than I would try to get her to a vet to get her stitched up. I have doubts that she will make it without vet care, but I have never treated a leaking air sac. The air sacs are how a chicken breathes in and pulls air throughout her body. Anything put into that wound can travel to the rest of the body, so that is why risk of infection can be so great. Antibiotics would be hood. Feed stores do sell procaine penicillin G in the refrigerated medicines under several brand names. With a 3 ml syringe with a 20 gauge short needle, you can give 1/4 ml once a day for 4-5 days of penicillin.