Get rid of the canvas bumper for a while. Get a wing and just play with her. Drag it in front of her, get her chasing it, but don't let her have it initially. make her chase you and while you're both moving, let her grab it but don't let go and keep walking/running. After a few steps, make her release it (with whatever command you use to have her give you the bird) and praise her like crazy. Lengthen the distance over a week or so. Then, go back and start over but let go of the wing. Keep calling to her and keep her following with wing in mouth but without you holding it. Hopefully, that'll help her forget about difference between the dummy and the wing. Then go back to your usual retrieving training routine but with the wing. Before you go back to the dummy, use a dead bird. Save a teal from a hunt or scrounge one, find a pigeon, whatever, just get her back to your routine with the bird.
A lot of work, but if she's got the goods, when she makes that first long retrieve in the field...it will mean that much more, and be that much more satisfying.
Post a pic. of your pup!