Welcome To BYC
Can you post photos of her?
The poop appeared to have blood in it, have you dewormed?
She doesn't lay eggs anymore - how long ago was that?
I'd still be inclined to give her Extra Calcium just in case she's struggling to lay an egg. Hens usually continue to lay throughout their lifetime, even if it's only an egg a year.
You can find Calcium Citrate with D3 in the vitamin aisle of stores like
Walmart, CVS, etc. Give 1 tablet daily, just pull down on her wattles, pop the tablet into the beak and let her swallow.
Check her crop to see if it's emptying. I'd work on hydration like you have been doing and then offer wet mushy feed.
It won't hurt to treat for Coccidiosis. Corid is found in the cattle section of
TSC.
Liquid Corid dose is 2tsp or Powdered Corid Dose is 1 1/2tsp per gallon of water given for 5-7 days as the only source of drinking water.
Do not add any extra vitamins/electrolytes that contain B1(Thiamine) to food or water during the course of treatment.
With her age, she may have something else going on, often older hens start to have some issues with cancer and/or reproductive disorders.