Can you post a picture? Whenever I have had a chicken who was becoming weak and dying, the other chickens would peck them and make combs bleed. She may be sick, so I would do a thorough exam of her crop, her droppings, feel her breastbone for weight loss, check her lower belly for swelling, look her over for mites and lice.
I agree that separating her in a dog crate with food and water, but leaving her with the others is best. Then when she is heling, supervise some visits out in the yard in the evenings before they go in to roost.