Q: Do I need to bathe my chicken?
A: Generally speaking, no. Chickens don't need baths. However, if they do get something stuck in their feathers that they are not preening out, you can choose to bathe them. Keep in mind that bathing should be kept to a minimum, since shampoos can be drying to their feathers and make them brittle. If the dirt doesn't come out with simple water, you may want to try a pet bird shampoo like one you can find at your local pet store. These are generally kinder to their feathers than what you might use on your hair.
Be sure your bird does not get chilled when she is wet. If it is cold in your area right now, you will want to be sure your bird is dry before you put her back in her coop. Lastly, most chickens won't like to be bathed, so be careful! She may scratch or peck. Bathing a chicken will also make a wet mess when she begins flapping her wings to object (and escape!)--so be prepared. It is probably a two-person operation, especially if this is your first time bathing your bird.