Greetings Donna,
First, let me say, it's entirely possible that the hen has something other than Marek's going on. There are other diseases and even nutritional deficiencies, that can cause paralysis. I just wanted you to be aware of possible scenarios. It's common for more than one thing to be affecting a sick chicken. So, as the keeper you have to keep an open mind.
Now, in response to your concern about Marek's, it's good that you separated the hen. Separating a sick chicken allows the keeper to conveniently administer meds, monitor progress, it also provides a quiet, safe place for the chicken to heal, and in some instances, protects the rest of the flock from infection. However, in the case of Marek's, the flock members most likely have already been exposed by the time a chicken shows any symptoms. There is a blood test to detect Marek's, but it is not accurate. Usually a necropsy is done after a chicken dies, and that confirms the diagnosis.
And then, there are the chickens that recover from Marek's, and are now carriers. Here is a link to an excellent article written here on BYC. It presents an interesting point of view regarding Marek's and is good to read. It will answer some of your concerns about reintroduction of the hen.
www.backyardchickens.com/articles/the-great-big-giant-mareks-disease-faq.66077/
I think it's good that you are giving extra vitamins to help the sick hen heal, just take care to follow product instructions. Boosting the chicken's immune system will also help. Since it is the immune system that will hopefully defeat any invading virus. I always include herbs to boost the immune system of a sick chicken. Goldenseal and Echinacea work together not only to boost the immune system, but can kill harmful bacteria that cause secondary infection. I have now added Manuka Honey, medical grade to add even more healing properties. But, even if you just administer some Echinacea alone, this is helpful. I will give you information on dosages if you like. Increasing the protein level is another helpful thing to do. Cooked meat, tofu, eggs, hemp seed protein, cooked peas, fish, etc., are good choices. Also, add fresh greens, cooked mixed vegies, and red and black fruits, diced up for easy swallowing and digestion.
Take time, to make the decision about reintegrating your hen. I know how hard it is when we have to deal with a sick chicken. I have done it many times. For the last 6 weeks I have been treating my entire flock of 8 hens and one roo, for Infectious Bronchitis. Each week one or two would come down with symptoms. Some became severely ill, and had to be put into the hospital crate for a couple of days. Then, some get well, only to relapse a week later. I could have just culled them all, disinfected the coop and be done with it. But, these are my pets, I don't depend on them for food or income. I will most likely wait for 6 months (the time recommended for IB)or more, before getting any more chickens, or I'll let my broody hatch some eggs, from the flock. The good thing is, I didn't lose a single chicken. So stay calm, be patient, learn more, and in all things, be grateful.
Like I always say, "Life on the planet...it ain't easy!".
These are some of my thoughts about your sick hen. I hope they are helpful.
God Bless
