@Kathy Sistare , There are so many things that could be wrong. Is she about 16 weeks old? Or younger? At around 17-20 months old, they go through their first big molt. They can act tired and out of sorts. Or she could have some reproductive issue, too many to name and too many have similar symptoms. There really is not enough to go on to even begin to guess what may be the issue with her. Supportive care would entail extra protein and vitamins in her food, like putting a few drops of polyvisol liquid baby vitamins *without iron* to her beak each day for awhile or in something she will eat. Most things, all you can do is lend supportive care. If she seems really ill, separate her into a warm location so she can rest undisturbed and you can monitor her poop and how much she is eating.
She appears to be a Wyandotte. Is she a hatchery gal? If so, it seems that most hatchery Wyandottes are very prone to reproductive malfunctions. I've lost all mine to those and won't have any more.