Help! Sick banty hen

I dont know if anything can even be done at this ponit, but here goes. About two days ago my bantam hen started lookin unthrifty. No other symptoms than lethargic and puffed up. No one else in the large pen is sick, and she's getting progressivly weaker. She's in isolation with free choice water, some corn I took out of the freezer and defrosted, bread crumbs ect. Shows no interest in these "treats." Any suggestions? She feels quite thin..

Check for mites/lice, around the vent, head and under the wings.

How old is she Swamp hen? I hope it is just something simple like bugs, but Mareks disease can also have symptoms like that. Usually young birds are affected. I bought a black Cochin pullet last year that became thinner and thinner and weaker and weaker although she was eating well... she just wasted away and I was told it was from a form of Marek's disease. There is not much you can do in that case but keep her comfortable and not let others pick on her.

Well, sadly she didnt make it. I made the decision to put her down when I came home Friday. She was "shockey," to weak to stand, her head kept kind of "twitching" sideways ect. No sign of mites that I could see, but I think tomorrow I will go out and catch a few birds for inspection. She was very very thin, which is odd, because I caught her and trimmed her nails a few weeks ago and she was not that thin. (I was well away from the quick, so I dont believe it was an infection from an open toenail) I thought Marek's usually had other symptoms, do you have any information about this "form"? Everyone else seems to be okay so far, hopefully it stays that way!

She and her man were a buy from an auction this spring, they were supposed to be year old birds, but I'm thinking/hoping perhaps the seller grabbed the wrong hen and she was just old?

What you need to do if another comes up with these symptoms is to do a necropsy on them after you put them down. If it is Mareks causing the sickness you will see tumors on the organs, look at the gizzard and intestinal areas for strange lesions.
If you find nothing then you know to look further for mites, lice, etc. Sometimes if it is a minor outbreak they are hard to see. Best is to go out a night, some mites leave their host during the day and come back on the roost to feed on them at night, also the chickens are resting better at night and easier to look at, finger through the feathers around the ears and vent, looking with a flashlight and you should see them if they have them.

Not trying to steal the post, but is there anything you can do for Mareks other than cull or does it spread like wildfire once it's on the property?

I was reading up on this the other day and read vaccinating is dodgy with success at best?

How was her crop? Is it too late to check?

Didn't get a chance to do an autopsy unfortunately. I did have a feel of the organs below the rib cage, wondering if she had a tumor or something. Obviously not as detailed as a visual inspection, but I didn't feel anything out of the ordinary. Her crop was absolutely empty Sue, again, no autopsy, but there was nothing in it for sure.