Welcome to BYC!
I am so sorry about your hen. Have you checked her for egg binding? You mentioned she waddles around. That can be a sign of a stuck egg. Put on a latex glove with some KY jelly on the index finger and insert your finger into her vent. If she has a stuck egg, you will feel it there. First break up some tums. They have calcium. Feed these to her. The high calcium can help her with contractions and move the egg. You can also soak her lower half in warm water for 10 mins. This will also help to move the egg. Both of these remedies usually get those stuck eggs moving.
If she is not egg bound, check on her outside between her legs at her abdomen. This area should be fairly firm and not squishy like a water balloon. If it is really soft, she could be internally laying or have reproductive cancer. Antibiotics can help with infections sometimes, but won't cure her of either of these conditions.
Has she been wormed lately? Worms can suck the life right out of a bird and can kill them eventually.
If you don't think it is any of these, then it could possibly cocci. Cocci will have them all fluffed up and lethargic. Corid in the water for 5 days would help with the cocci.
I would also check her all over for other issues like mites, crop issues and anything else that might send up a red flag.
These are the things that I would do, look for and consider. Hopefully others respond in the emergency section too.
For now, get her under some heat. Sick birds are cold and don't heal well. I hope you can get her healed up soon!
and Welcome To BYC! Sorry about your hen, hope you are able to figure out what is going on and she recovers.
