Drooling is a big sign- seems I read it could be an impacted crop or worms-something causing her to expel drool. Hopefully someone with experience in this will chime in. I know it is tough when they are struggling.
Just re read your post- she is drooling? That is odd.
I found this:
Post in thread 'Chickens drooling and lethargic, HELP!'
https://www.backyardchickens.com/threads/chickens-drooling-and-lethargic-help.1418945/post-23311550