10-12 week old sick hen, help!!

[Valmai]

I got these 4 10-12 week old chicks a few days ago and one of the hens has already fallen sick . She has become very lethargic, keeping her eyes closed (sometimes she only keeps one closed), I have seen her sneezing and coughing several times. I isolated her from the other 3 and it breaks my heart to see her making loud noises just because she can't see her friends. What must I do to help her get better and what might've caused it? It's really hot here so I can't see her getting a cold (31°-38°C).
Are there any "natural" ways to help?

 

[_-Captain BRM-_]

Could you send some pictures of her? That always seems to help for evaluation.

 

[Eggcessive]

I would keep her with the others that came with her, but quarantine them from your other chickens. Do you see any bubbles or foam in an eye, or swelling of the eyelids or face? Sneezing or coughing sound like she has a respiratory disease which are spread by carriers most likely from where she came. Have any of your other birds ever had a respiratory infection?

 

[Valmai]

I would keep her with the others that came with her, but quarantine them from your other chickens. Do you see any bubbles or foam in an eye, or swelling of the eyelids or face? Sneezing or coughing sound like she has a respiratory disease which are spread by carriers most likely from where she came. Have any of your other birds ever had a respiratory infection?

Nope, never, there 4 are the only birds I currently have really at the moment. I didn't see any bubbles, foam or swelling.

 

[Valmai]

Could you send some pictures of her? That always seems to help for evaluation.

It's 10 PM at the moment, I can send in the morning if that's fine?

 

[_-Captain BRM-_]

It's 10 PM at the moment, I can send in the morning if that's fine?

Sure, it just helps for me at least to see the chicken

 

[Valmai]

Sure, it just helps for me at least to see the chicken

I would keep her with the others that came with her, but quarantine them from your other chickens. Do you see any bubbles or foam in an eye, or swelling of the eyelids or face? Sneezing or coughing sound like she has a respiratory disease which are spread by carriers most likely from where she came. Have any of your other birds ever had a respiratory infection?

Soo.. It turns out, all the chickens are sick, not just her (The red one was the one I originally asked about), only one of them looks kind of okay to me (The blue legged red one). The rooster is sick as well but not as much as the blue and red one.

I noticed some "swelling" underneath her beak throat area after some observation. She also kind of like opens her beak and stretches her neck upwards like she's trying to get something down her throat or like gagging idk it's confusing I just hope she gets better