I’m no expert but I believe your hen is in her last days, hours. I know her beak is a little longer than normal, but I also believe her major problem is inside of her. I have had two hens to die on their own and two others that I had to euthanize. I did a necropsy on all four, only to find problems that no vet or medicine could have cured. Three of my hens were filled with tumors and one had Egg Yolk Peritonitis (EYP), all fatal illnesses. IMO, your girl is doing what a declining bird does, pulls away, and stops eating (not because of her beak though.) And what you are noticing with the more and more prominent keel is her wasting away. Feeding her now is only prolonging things. I would go ahead and call in your back up to euthanize her. She is not well and nature is taking its course.
I truly am sorry you are going through this, but unfortunately it is part of being a responsible flock owner. Best of luck to you and your girl.