It's been 5-6 months and she may improve. If you think her quality of life is poor, I would euthanize. But, seems like she's happy at this time. I've only had 1 hen that had Marek's paralysis and recovered and that was 3 years ago. It took her about 2 months. I never thought I would see one get better.
I've had a nearly identical experience with a rooster. It took him a long time to get his legs back working, and they still aren't right, but he can get around and has a good quality of life. I suppose it really comes down to that-- if their quality of life is good, I let them stay around and we enjoy each other's presence very much for the time my bird has.