Does anyone have a clue what I can do to help her?
Sorry your hen is having issues.
So did the vet run a fecal float to test for worm type or load before suggesting that you throw unknown fixes at an already ailing hen that might mask symptoms of the root cause for her condition?
Sounds very much like your hen is facing reproductive disorder of some type. Possibly internal laying, egg yolk peritonitis, ascites, cancerous tumors, organ failure, or other. Prognosis is poor just due to age and breed alone.

But let's see if there IS anything at all that we can do to help.. Please pick her up and give her a good once over... is her abdomen swollen, what is the color of the skin around the vent and the condition of the feathers there? What is her usual feed including treats and supplements? When was the last time she laid an egg? You say she is still eating but not passing normal droppings.. Is she also still drinking?
If her appetite is good then her crop may be functioning fine. If there is reduced appetite then I would definitely check in the morning before food and water to see if it's fully emptying over night.
What is geritol.. a human vitamin? Is this vet familiar with avian health at all? Are you in the US? Please add your general location to your profile as it can help folks make their best suggestions possible at a glance.
Did you see ANY worms in poo before or after worming? What did you worm with?
You describe her definitely as lethargic.. which is indicative of more than a possible foot or leg injury. But have you looked her legs and feet over for any kind of bruises, cuts, swelling, or heat that might indicate an infection?
What antibiotic did you start last night? Is she staying out with the flock or have you separated her already? Is your electrolytes a packet one?
All my questions and suggestions are only meant as helpful not judgmental. There are no wrong answers.
Hope she recovers quickly!
