Newspaper is better than nothing, although if you can find paper that doesn't have printed ink on it that's probably best. Anything that's warm and dry is better than what she had.
So as to your other question. Yes, probably taking her to the shelter without her consent is technically theft (at least where I live) because you're intentionally depriving someone of their property. That's why I originally suggested telling your roommate the chicken died. I'm just trying to do what's best for the chicken here! And really, at this point, it's looking more and more like the chicken might die in reality. If you wanted to do it the 100% legal way, you could call the animal control division of your police department and explain what's been going on. Since the chicken sounds (and probably looks) like it's obviously suffering to a great extent, the animal control officer will more than likely take custody of it and bring it to a vet or a shelter (that's what happened at the department for which I worked).
So other than telling your roommate the chicken died and taking her to a shelter, or calling the police/animal control tomorrow, the only other option I can see is doing what you already are - making the living conditions actually livable at your own expense and labor. Doing one of those three things is the only way the chicken is going to live. At a minimum, she needs proper shelter from the elements, which includes some sort of bedding (pine shavings or straw, don't use cedar or sawdust), a feed made specifically for chickens, fresh water, a dwelling that doesn't accumulate ice, and space to move around in (at least 25 square feet outside, like 4 square feet inside).
Oh, I just thought of a fourth option - you could bring her to an emergency vet, tell the vet exactly what's going on in great detail, and hope the vet will recognize an abusive situation when he sees it and confiscate the chicken.