desperate for ideas

[RIRNHRBASLW]

I have a black Australorp pullet 7.5 weeks old. Last week, she was a little less active and got stepped/walked on by a NHR; she was able to get up after I shooed him off, but limped a lot. I looked her over and confirmed no major injury or slipped tendon. I wasn't sure about foot, as it looked like early bumble. I cleaned it, applied antibiotic ointment, and bandaged as precaution, then put her in our "healing pen" (slightly raised wire box with padded floor to allow max social contact while protected from further injury) inside the coop. The next couple days, I treated for bumble and her foot completely healed by Thu, although she was Very unsteady on her feet and preferred to list toward her left side when lying down. She was supervised when in general population, but still not very active; I added a very docile friend for comfort when I put her in. By Sat evening, she was not making much effort to stand, consistently fell to left side, didn't preen herself, and seemed to be having difficulty with her left wing. Her feet and tendons were fine, and she hadn't been picked on or unduly stressed; she was still eating and drinking normally. Yesterday, she was laying on left side, no balance, and could only propel herself in circles with her feet. She could still reach food and water, all normal processes and feces. This morning, she seemed even weaker and has obviously lost a good portion of her meatiness, even though her appetite hasn't waned and she's been comparatively sedentary. I've done (a Ton) of research, but I'm not sure what this is, if it's contagious, or how to better treat it. Marek's was my focus, but no white spots, abnormal feathers, diarrhea, or diminished head control; also no known cross-contamination or potential contact from others. Any and all insight/advice is greatly appreciated! Thank you!!