Help with sick chicken?

I have 19 chickens. 14 are one year old, and 2 are 2 1/2 years old. Maybe a week ago I noticed one of my hens a 1 year old Easter egger not acting like herself. Just sitting on the roost for a couple of days. I took her down, took her to the food, and right away other hens bullied her away. I put her in the little pool. Normally she would have instantly jumped out, but staid a bit then drank a while. She tried to eat and was bullied away again.  I put her in the chick wing by herself for 2 days, then she seemed better, wasn't getting bullied, so I opened up the chick wing. I have been keeping an eye on her. She doesn't have anything obvious wrong, but something is, more than being at the bottom of the pecking order.  She eats and drinks, but not much. Normally if I put food in front of her she would go to town, but now she doesn't eat it, just walks away.  I have seen her eat a little. The 2 days she was isolated I found no eggs.  Today she is constantly shaking her head.
I have been looking online. The only thing that pops is mites, but this seems more serous than that.  I'm going to treat the hens and coop for mites, just in case that's the problem.  I'm going to try to feed her some oregano, and scrambled eggs, and garlic to try to give her a boost.  Wait and see.
I would love any ideas. Thanks

No eggs? Any chance she is egg bound? Perhaps keeping her isolated would reveal if she is still not laying.

I don't know much about the condition myself beyond the following: DO NOT break an egg that is internal or still within the bird (infection and death are common); I think (please check with someone more knowledgeable than me!) that warm water soaks can be helpful.

Is she broody? Does she have a raised or lowered temperature? What does her poop look like (normal?). This would be helpful information.

I guess I need to isolate her again.  I don't think she is broody, I don't know if she has a temp, she didn't feel warmer than the other chickens.  I thought maybe she wasn't laying because she isn't eating much.
Tonight I spread DE all over the coop and chicken yard. (I read shaking head could be mites. I have noticed more scratching, and cleaning hens) I also put it on my sick hen. She did eat some of the DE.  I didn't see any of the other eating it, maybe she knows she needs it?   I tried to give her some egg with garlic and oregano. She wouldn't eat it. All the other chickens went nuts for them.
I just don't know.  I have seen her eat, drink, poop looks normal. She was with all the other hen both times I went into the chicken yard, and no one was picking on her.  I still feel something is wrong.  Once a day I feed then fermented grains (there is always layer crumbles). Yesterday I had a bad headache and didn't go out. Today I was later than normal. The crumbles were gone.  When I fed them you would have thought they were starving. My sick hen waited until everyone was done, and ate a little fermented grains.
Tomorrow after work I will put her in the chick wing. Cook some more eggs for her. Maybe she will eat it if it's in the feeder. She is one of my more timid hens.  The first time I isolated her she seemed back to normal after only two days.  Last year before I get these newer chickens, 4 of the chickens picked on one so bad she would spend the hole day in a corner. I ended up letting her out of the coop. She lived happily on her own for months.  At some point when the chick were big enough to be integrated with the older hens I put the outcast in the coop, and for some reason they left her alone.  So I also wonder if she isn't sick, but just being kept from the food.  Oh how I wish I was Doctor Dolittle. I would just ask her.   Thanks

Just the stress from being bullied too much might be enough to make her sick. I've seen that happen before.

Hi Jen,
It is tough to see a sick animal and not be able to figure it out. I do know that animals, particularly birds, will hide an injury or sickness as much as possible for as long as possible. The rest of the flock can often tell and will try to drive away the weak or sick bird. I have a feeling your flock knows this bird is sick.

From another forum on raising chickens in your back yard :), I won't mention the name... I found this quote.

Head shaking can be a sign of a respiratory infection or disease, ear mites, or ear infection. Some types of head movements can signs of crop problems or adjustment, or neurological in nature.

Is there any discharge around the eyes or nose that might signify a respiratory infection as opposed to being eggbound or having mites?

Usually even the lowest hen will still get in on the food, but it is recommended to try two feeders (or if feeding on the ground, spread it out more) so as to afford the lowest chicken a better chance to get some food without being chased away.

I don't know how to check, but a plugged up crop would probably reduce how much the chicken wants to eat... and if it went on for long enough would make the chicken weak... though you said she acted normally after a couple days in isolation, so that shouldn't be it.

Sorry for the couple edits, but I kept thinking of other things. There will always be a pecking order, but if you end up suspecting it is due to being bullied vs an actual illness, then you might try to give the flock a larger area to be in, and/or put in more things so the chicken can hide and be out of site from the more dominant birds. Birds that are cramped or bored will do a lot more picking. Chickens that are busy scratching or playing won't have as much time to pick on each other.

Just some thoughts. Let us know what you find or if something changes.

I'm sad to say she died today.  I never figured out what was wrong with her.  She just didn't fit any of the things I researched.  I treated her for mites, along with the coop, she ate DE. The strangest thing was she would seem better some days, and I would think ok she's on the mend, next day she would be lethargic, and seem sick.  Three days ago she was acting normal, excited about food, and holding her own with the other hens.  Two days ago she was laying with one wing extended. I could tell she was doing poorly.  I soaked her in warm Epsom salt water, gave her sugar water. She made it through the night. I treated her this morning, but she died while I was at work.  The thing that ways on me is I know she suffered.  I should have probably dispatched her last night, but she bounced back before, so I hopped she would be ok.  
In 17 years I have never had a sick chicken.  It's terrible not to know what's wrong, and how to help. Can't afford to take her to the vet.  All the other chickens seem to be healthy, so I can only hope what ever was wrong didn't spread.  
Thank you to everyone who tried to help. It was appreciated.

Hi Jen,
I'm sorry to hear about your loss.

If the other did not catch it after a week of interacting with that bird, I doubt they will. This would make me feel confident that whatever it was, was not contageous... or that the other chickens already have immunities against it.

Thanks Matt, that helps ease my mind a bit.  

The ground was so hard I couldn't even bury her.  I have a lemon tree that has needed to be planted for months.  I chipped away enough soil to form a small hole, and left the hose on for a couple of hours.  I ended up digging an extra large hole, buried the hen, and planted the tree.  It felt like a positive way to honor a sweet hen.  I'm glad she isn't suffering anymore, but still wish I could have figured out how to help her.  So many people lost chickens this year to heat, and I managed to get my girls through it. It stinks to loose a hen to sickness.  I think it is the not knowing that makes it so hard to except.  On the positive side, all the other hens seem very healthy.  I hope they stay that way.