Hi
I have a young pullet, Hopsy who is like this, although the problem was more that she lost confidence and would hide in the nest box from them rather than that thy were picking on her. She has been lame as a result of Marek's disease for the past 4 months and is bright as a button apart from her lameness. I keep her in a brooder box in the hen house and she has been very happy in there as she can still see the others but feels, not only safe but from her attitude, I believe rather privileged, like the queen in her palace and I am her humble servant. A few weeks ago I had another pullet develop quite severe paralysis with Marek's and she too has been placed in the sick bay with Hopsy. After initial aggression by the new inmate, the 2 of them are now palled up a treat and are best buddies. The newer one's condition has improved enormously in the past few days and I have even been able to put them out in the sunshine a few times recently and because they now have each other, their confidence is higher and they are not intimidated by the rest of the flock. My flock is free range though so the others have plenty of space and things to keep them occupied, rather than picking on the invalids.
I appreciate you don't have another poorly chicken to pall her up with but perhaps a lower pecking order, docile hen would work if you can rig something like my set up.
My sick bay/brooder is actually an old sideboard with the drawers taken out (I use one of the drawers as a sick bay nest and the others as nest boxes and I made a mesh cover to replace them. I cut large holes out of the double doors in the middle and covered them with perspex, so that plenty of light gets in. It works brilliantly for both sick and broody purposes and I can partition it up, so that I can have 2 broodies in it at once. Alternatively you could perhaps build/obtain a small hen ark and place it either in the run or next to the run for the lame girl so that she has her own quarters but can see the others.
Anyway, I hope this post has given you a few ideas and good luck finding a solution that works for you and your little hen.
Regards
Barbara
PS. Expect some teething troubles with whatever you set up and be prepared to tweek things to make it work.