I just wanted to point out that he preen or oil gland is in that area, and that she will preen herself there and spread the oil on her feathers. Did you try any of the ointments that I suggested in the earlier post? Many have good luck with Nustock, pine tar, bag balm or even petrollium jelly, because of the taste and the sticky ointment.
I have made one piece no sew saddles out of polar fleece that slip over the wings and held on that way. A 2 inch slit on each side in a piece of 7x9 inch fleece works well, and can be trimmed once it is on. Here is a link with instructions and mine look similar:
http://www.linnacresfarm.com/2014/04/how-to-make-simple-hen-saddleapron.html
At first when they are put on, the other chickens may freak out a bit, but they settle down pretty quickly