Dead hen in laying box

[BlissInBelize]

Hi all, I’m hoping someone might be able to help. I went out after lunch(it’s incredibly hot these days) to collect eggs from the chicken house. One of my hens who has been quite croaky & seemed to have respiratory problem a few days ago was lifeless in one of the laying boxes. She seemed fine this morning when I let them out & I stayed out with them to check on her breathing since I was concerned about her a few days ago.
no one else seems to have this issue but an old rooster we got rid of a few weeks ago. Should I be concerned for the rest of the flock? Is there anything I can give them as a precaution so this doesn’t happen again.

 

[Sally PB]

Would you be comfortable doing a necropsy? I'm assuming you're not in the US, so I can't suggest sending her body to a lab.