Help! Marans hen with purple comb

Can anyone give some advice? We’ve had our girl Octavia for about three years. She isn’t the most energetic chicken but last Friday we noticed she seemed a bit off/slow, and over the weekend she has become slightly more sluggish. Her comb went from slightly purple (Friday) to much darker (Monday), and she’s also been off lay for a few weeks. There’s also a photo of how she looks normally.

She’s still eating and moving around, her vent is fine and her crop is also fine, but otherwise doesn’t seem very happy. We don’t have a vet nearby that specialises in poultry and the Internet says the purple could mean circulation issues, so we’re a bit worried about her. Does anyone have any advice about what we could do?