My hen is about the same age as yours with the same symptoms. In my last ditch effort I started giving her doxycycline with lots of water. I diluted hard boiled egg yolks with water so I could squirt small amounts into her mouth. I went into her coop the next day, not sure what I’d find, and surprisingly, she seemed a little better. Repeated routine, gradually increasing more eggs. Soon she was eating on her own. She’s out happily free ranging now and almost back to her old self again. She still has a ways to go but I’m so pleased with her recovery so far. Thank you for sharing your experience. I appreciate the feedback