I agree, I'd give her the Calcium and see if that helps. Being hunched up along with an ammonia odor, I would suspect something reproductive. Most reproductive disorders can cause similar symptoms, so it would be hard to know which one unless the hen dies and necropsy is performed.
Deworming and treating for Coccidiosis probably won't hurt, I would not deem either of them as aggressive treatments. As long as dosing is correct, dewormers like Fenbendazole and Albendazole are well tolerated as is Amprolium that treat Coccidiosis.
