I had a three year old hen with those exact symptoms. She died a day later, vet confimed coccidiosis. She showed no symptoms until the day before she died, she wasn't eating much at all but was drinking like crazy and had very watery poop. When I picked her up to examine her that last day she was so full of water she threw it all up. No blood in the poop at any point. I had a couple more start looking puffed up the next day but I started the whole flock on Corid and everybody else cleared up fast. Egg production went up almost immediately.
WIthout testing you can't be sure of what your hen has but I would treat immediately with Corid and then when you are done with that deworm everybody and give probiotics. You can find Corid at most feed stores, mine carries the water soluble powder 20%, labeled for calves. Dose is 1/2 tsp per gallon of water for 5 to 7 days. Treat the whole flock. I would use Corid and not any of the sulfa drugs like Sulmet. Very harsh on the birds systems. Corid is much easier on them.
I personally don't bother with Wazine, it only kills round worms and there's a lot more junk chickens pick up. I use Strongid, Valbazen and Eprinex on a rotating basis. Unless you want to use Wazine first to get rid of some worms if you think they have a heavy load, then follow up in 10 days with something better. No matter what you use you need to do a repeat in 10 days to clean up anything parasite that was in egg/cyct form the first time.
Valbazen is liguid, you give 1/2 cc orally for standard chickens, 1/4cc for bantams. I use little one ml syringes, no needle to squirt it in their beaks. Eprinex I use topically between the shoulders, same dose. Dose for Strongid escapes me at the moment, I'll have to look it up.
You will need to move fast if you want to save your hen. They hide their illness until they are feeling so badly they just can't do it anymore. So by the time you are seeing visible, obvious symtoms you have a very sick bird.
Good luck, I hope this was helpful and that you are able to pull her through. I'd worry first about coccidiosis, it kill's fast if that's what it is.