They also do free range but my one turkey can hardly move. I had the same issue with a turkey I rescued. She was paralyzed due to a weak heart (took her to 3 different avian vets). She ended up dying. The vets said there was nothing I could do. I just made her comfortable and gave her fluids since she wouldn't eat. I'm afraid my current turkey is suffering from the same condition. But I have her in the house at night so I can make sure she's getting water and feed. She's eating at least. I put the rooster booster in her water should I just give her a mix by syringe at this point?
If she's drinking I think that would be sufficient. I mix it stronger for babies and the ill.
Have you checked her over for any injuries? You say she can walk but it's like it fatigue her quickly, right? And she's coughing but does her breathing seems labored? Sneezing? Nasal discharge? Trouble swallowing?
Is this bird from the same place as the other with a weak heart? Are you sure it's a heritage and not a meat bird? It seems peculiar to be in such a situation twice. Meat birds have many health issues and are not bred for hardiness, with, I think, a six month lifespan.
You may consider antibiotics, which I think can still be bought OTC, but i don't have experience with selection and dosing. Hopefully it is just an infection she is fighting and all she needs is your TLC while she fights it off.
Sorry I can't be more help
