If there is a history of Marek's in your flock, no chicken, no matter what the age, is safe. All it takes is a stressful situation and Marek's will take hold. The age limit doesn't hold true. It is said that chickens are immune after 25 weeks of age...but, there are many of us that will tell you that is a bunch of bunk. Vaccinate your adults, just to be safe.
A little improvement; She's gotten a bit more active (shuffling herself from side to side with her wings every now and again.) Her stool has also gotten notably more solid, less discoloured, and not as smelly, I also haven't seen any blood in it (still don't feel smart for not treating for that immediately.) I started giving her a multivitamin supplement (with no iron) yesterday that has vitamin E in it, and I've been adding it to the distilled and deionized water I put in her chick-mash. Albiet this may dillute the solution a little, but it's still getting into her system nonetheless. Nothing new on the paralysis side of things, still just as immobile as when I started the thread.
Let me know if any of this sounds wrong, I'll change my approach ASAP.