Hi is the silver skin still there? If it is and the muscle is covered you can get a horse antibiotic spray. It forms a physical barrier on the skin.it keeps it moist and keeps out air and bugs and bacteria. I used it on a goose that my dogs got to. They pulled the neck skin and the skin just rolled down leaving only the silver skin. It grew back feathers and all. If it really is down to the muscle itself I'm not sure there is much you can do. She will probably succumb to shock or gangrene if you don't cull her. As to why the dogs went after her, being a game hen she might smell different? My lab was so good with the chickens. He didn't chase them and they pretty much ran him away. I got 2 guineas and within a week he ATE both of them. Not like your hen, nope I caught him chase one down and swallow it whole! Legs, beak, every thing he didn't even get sick! I was so mad but he just looked so pleased with himself, like, look I got rid of that weird critter! Needless to say that was the end of my guinea experiment. I'm sorry about your hen its hard to feel so helpless