Sorry to hear about your hen.
How old is she? I have Marek's in my own flock so I know a bit about it too. One of the things is that it mostly affects young hens in their first year and is often triggered by stress.... perhaps the additions of new birds to the flock, a cockerel's unwanted attentions or the confusion of the onset of egg laying.
Not saying this is or isn't Mareks that your hen had but it's less likely if this is an older bird and she does look quite mature. Might be worth trying a vitamin supplement as I've read that Vitamin B deficiency can cause paralysis.
I have had cockerels completely recover from an attack of Marek's and pullets that recovered from one attack only to get hit by another several months later. Thankfully my strain isn't as virulent as many others I've read about and I'm not suffering huge losses to it. I allow my hens to raise their own chicks (unvaccinated) within the flock and perhaps that is building up some resistance to it but I'm always vigilant for symptoms. Mine usually start with paralysis of one leg and they limp on their hock on that side. Sometimes they deteriorate rapidly, sometimes they recover within a few days but then have another more serious attack later. I spent weeks/months nursing two pullets with it last winter. The crucial thing I found was keeping them happy. Having the company of a pal and access to sunshine and grass whenever possible caused huge improvements in their condition but obviously the weather is not something you can buy at the pharmacy or feed store.
Unfortunately if it is Marek's there is no cure and the choice is to cull or offer palliative care. I have done both and will offer care as long as the bird has a decent quality of life but cull once things go too far.
I hope it's not Marek's for you and your flock's sake but it is an extremely widespread and easily contracted virus (it can even be wind born) so the likelihood is high that if you have chickens (especially young ones) experiencing paralysis, it will be Mareks.