I would get someone to hold her while you take a good look in the ears for the bugs. It may be infection(?)
If there are mites in there, put 1 drop of Peroxide in each ear (only 1 drop!). Hopefully that will kill what's in there.
Have you looked inside her ears?
Were you able to find vitamin E and B-Complex?
If you dusted her, then for the most part that should take care of bugs. Shaking the head can be part of a neurological problem.
It's hard to know if the ticks have caused her symptoms or if she's suffering from Marek's.
I would still treat the coop/run and birds with a Permethrin based poultry spray or dust. While the adults may live off the bird, the larvae can live on the bird for 2-7 days feeding off the bird...
I'm sorry to hear about your hen.
How old is she?
How long have you had her?
Did you find any ticks on her? Have you looked in her ears to make sure they are not in the ears?
For the ticks, I would clean out the housing and treat with a permemthrin based poultry spray or dust. If you notice...