If you haven't already, I would suggest posting about your injured hen in the emergency section. You'll probably get responses much quicker!
https://www.backyardchickens.com/forums/emergencies-diseases-injuries-and-cures.10/
When there are no signs of a wound or blood, try checking the neck for two puncture wounds. This is often how weasels kill their prey, by biting the neck and drinking the blood.