With regards to internal parasites, you could drop a poo sample off at the vet’s for examination. Our vet only charged £5 or so for the honour.
Coccidiosis can most definitely be a problem
without there being any blood in poo, no blood does not equal no heavy cocci load, but she would feel ill which yours doesn’t appear to show. Again, your vet could tell if there’s a light or heavy cocci load if you could drop off a poo sample.
Very yellow poo, sulphur yellow, is a sign of blackhead which is fairly innocent in chickens (deadly to turkeys), you could google photographs of it to compare to see if it’s similar. Your hen might merely have a few minor issues or a single 24h bug, hopefully she’ll perk up in the next few days. Good luck