To me this sounds like a case of Wry Neck. If her head seems to be tucked to one side or the other, or behind/under her, it is most likely Wry Neck. This disease is believed to be caused by a vitamin deficiency, and if this is what she has it was most likely caused by the mites she recently recovered from. Because you caught it early, you may be able to save her. What you can start with for treatment is Enfamil Poly-Vi-Sol, without vitamin E, a few drops daily, mixed with about 1/2 of the dropper full of Nutri-Drench livestock vitamin liquid, given to her orally. One of the most important things is to keep her hydrated, as dehydration will kill birds quickly. In addition to this, Selenium with Vitamin E gel capsules should be given, though you should research the amount, as Selenium overdose can be deadly as well. We had to order these on
Amazon, but if you can't find them, Vitamin E gel capsules mixed with about a bit of a Selenium tablet (again, I don't know how much your hen would need) can be a substitute. To counteract her diarrhea and to prevent her losing weight, vanilla yogurt with electrolyte powder is great for birds. You can also give her what we called 'Muffles Mush'. It is layer pellets, sunflower seed kernels, mealworms, vanilla yogurt and a splash of electrolyte powder ground together into a grainy paste (you can add water if it is too thick) and hand fed to the hen through a pastry icing bag. From personal experience, this helped my hen, but unfortunately she was 9 years old and weakened from previous problems and we were unable to save her (her name was Muffles). I hope this helps, and if you have any questions, please do not hesitate to ask.
~MisFitzFarm