Broody hens loose the feathers on their bellies, it is natural. That way they can keep the eggs warmer, and they feel hot underneath after they lose their feathers. As far as the other two symptoms, they are probably from her sitting and not getting out in the sun and eating and drinking regularly. But don't think she is "broken". I've had hens sit for five or six weeks before I gave them eggs, and then they incubated them for the three additional weeks, raised the chicks and went back to their normal egg-laying.
If you aren't going to use her for hatching eggs, I would break her up. It is quite an ordeal for a hen to sit, she doesn't eat and drink as much and she gets skinny, so if you don't need her for everyone's sake break her up!
What I do is put them in a completely wire rabbit cage, or a solid bottomed cage flipped upside down, and set it up at least an inch, the higher the better. Give her food and water! Anyhow, this way the air flows underneath her, which she doesn't like, because in her mind she is taking care of real eggs.
Also it depends on the person - some people put them in the dark then, and some put them in light. I prefer light, it is the opposite of what she wants while setting. Not direct sunlight, you don't want to cook her, just not any dark corners. After a few days she should seem more normal, and eventually she can just go back with the rest.
Hope this helps! MW