Blind chicken

Hi guys, I have two hens at the moment. One is an ex battery hen, we've had her for about a year and a half - I'm guessing she is about 3 years old. The other is a light sussex and we've had her for.....well, a long time. At least 5 years so she is probably about 6-7 years old.

One evening a few months ago, I found the sussex outside at dusk sat by herself. She didn't seem to want to move, even though the other hen was inside so I picked her up and put her in the house. In all honesty, I didn't expect her to make it through the night as I thought she had gone off her legs or perhaps had some kind of stroke. The next day however, she was totally fine so I was really pleased about that. I noticed over the next few weeks though that she seemed off. Her behaviour changed just slightly. She got a lot calmer (she didn't used to like being picked up but now doesn't mind) but she also did some weird things. I threw some corn down for them and instead of pecking at the ground, she just kinda wandered in circles over and over again. This sorta backed up my stroke theory - I thought maybe she had a period of restricted blood flow to her brain and it just made her go a bit....strange.
Now we have been keeping them inside the coop what with the bird flu thing and I noticed her behaviour got worse. She is still eating and drinking but she seems to peck the air a lot just above her food bowl. She does this with the water dish as well so I just nudge her head down and she eats/drinks. The other day I was cleaning them out and she walked into my leg twice.

I checked her eyes and they are clouded over. The pupils seem a weird shape - they are not round anymore. She has no discharge from them, no scabby bits, her weight is good and she can find her food/water and is eating/drinking as long as I leave the dispensers in the same place each day. She can see sudden or fast movement as far as I can tell - I dropped something in front of her and she jumped/backed away from it. She poops fine and her comb is a nice pinkish red colour.

I can only really think this could be ocular mareks disease but I dont know how likely this is what with her age. The other hen is not affected in anyway at all. I am not able to go to a chicken vet as there are none around here - my local vet knows nothing about chickens. I'm a bit stumped really. I thought if it was mareks and it had started that night a few months ago when she was sat outside, she would have died by now or at least the other hen would be showing the same symptoms?

I do not want to cull any of my chickens if possible. I don't mind looking after a blind chicken at all. My main concern is that I am moving house in a few months time and there will be at least a one month period where my chickens are going to live at someone elses house for a while (I will have no where to keep them while I am waiting to move). They already have chickens so I can't send them to someone else if they have a disease. I really don't want to put them to sleep on the off chance one has mareks as I know there isn't a test for it until post mortem....at the same time, I cant risk someone elses hens. I'm very confused/upset about this.

Any advice?