Help! Urgent! Chicken lethargic, not eating or drinking

I have an approximately 2 year-old sexlink. She is very lethargic. My husband let the girls out of the coop this morning at about 6:30 AM and when I looked out there at 8:00 she was standing in the middle of some grass and wasn't moving other than to put her head down every so often. She appeared to maybe be drinking some water off of the grass. After watching her not move for about 10 minutes I walked down there and got some scratch out and called them over. The other three came but she stayed right where she was. I walked over to her and she just stood there and looked up at me. I picked her up and she didn't make any effort to struggle. She will let you pick her up sometimes but she usually puts up a little fight first. I noticed that her back end is very dirty and the feathers seem almost glued together. Other than that she didn't look any different than normal. I put her down by the other girls and she didn't eat any scratch. I got her a bowl of water to see if she would drink. She didn't touch it either. Last night my husband gave them some red grapes and some lettuce but I don't know if she ate any or not. She seemed fine yesterday but she did seem to be a bit of a loner later in the day. Usually all four chickens are roaming about their yard together. Her poop is pretty runny although it looks pretty normal. It is mostly white with some blackish gray color to it. I have four chickens and I can't say that any one of them have the same looking poop right now. She quit laying eggs about a month ago after giving us eggs sporadically. She has laid a couple of eggs without shells that we know of a couple of weeks ago. She looks like she is going through molt, and has looked that way since early fall of last year. They have a 6X6 foot coop with two nest boxes. We use wood shavings in the nests and on the floor. Their normal diet is laying feed. We give them yogurt and oatmeal mixed with a little scratch every 3 to 4 days. They also get occasional treats like grapes, berries, or some vegetables. They have a fairly large area to roam around in and eat the usual worms and bugs.

Earlier I gave her a bath and that seemed to have helped a little. She is definitely moving around more. She is drinking some water and eating quite a bit of grass.

Can anyone help with a diagnosis? Any input would be most helpful.

When you gave her a bath did you notice any bugs? Lice and mites will make them lethargic and can kill them. Look around the vent, under the wings and along the neck. What color are her comb and wattle?
Try to keep her from eating grass if possible. She could get an impacted crop. Instead try to get her to eat some scrambled eggs, yogurt or wet cat food if you have it. Something with high protein.
I would start her on a vitamin and mineral supplement such as Poly-Vi-Sol w/o Iron (Available at your local supermarket in the infant section).
What other symptoms or signs is she showing?
Droopy wings
Ruffled feathers
Swollen eyes
Nasal or eye drainage
When was the last time that they were wormed? If it has been a while or never you can give them all a run of Wazine 17%

We have never wormed them that I know of. My husband may have but I don't think so. I looked pretty close and I didn't really see anything that looked like mites or lice. She closes her eyes quite a bit like she is going to sleep and they look a little puffy. Her comb and waddle are red. Her skin looked pretty much fair/white except in the area that was rather dirty and gummed up. It seemed pretty red. Her feathers seemed a little ruffled this evening but her wings didn't seem droopy. She is locked up for the night so she won't be eating anymore grass. I will get her some Poly Vi Sol tomorrow and get worm medication also. What if she does have mites or lice that I just can't see? What can I do for that problem?

Thank you for your help.

Keep her seperated from the others in a quiet area. just in case if she has something contagious.
If you pick up Poly-Vi-Sol tomorrow, make sure it is the one without Iron. You can put a few drops in her water or better yet put a couple of drops on the side of her beak so that she drinks it. They don't like the taste of it.
You can worm them all by putting 2 tablespoons of Wazine in a gallon of water. Give that to them as their only water source for 24 hours. After the 24 hours they can go back to regular water. Do not eat the eggs for 10 days unless you need worming also.
Lift up the feathers in different areas and see if you see any light brown bugs scurrying around. They are quick and sometimes hard to see. They are smaller than a grain of rice. Those would be lice. Mites are usually found around the head. If they do have either you can use many different products that help. We choose to use Sevin dust but many people will tell you differently. You can also Diatomacious Earth (DE). DE is a natural product.
You could start her on a broad spectrum antibiotic but you don't really know what you are fighting. We tend to put our sickies on Sulmet or Corrid to start if we can't determine what they have. If there is no change then we switch to another antibiotic.
Unfortunately with chickens, by the time you see symptoms of something wrong, whatever it is is in a pretty advanced stage.
Listen to her breathing as she rests. Is there any gurgling or weezing?
Watch for even the slightest signs of something different.

Is it possible to give the Solmed and the de-wormer at the same time or does it have to be done separately. I ask because both need to be in the water.

Do them seperately.
I also answered your email