I am so sorry this is happening. I know how stressful it is.
You can get a lab in Texas to do a PCR test on a swab (just like a Covid test).
It costs $20 a test - you should test for more than avian leukosis and they can do that on one swab.
You do have to buy the swabs - another $20 for 10 I think - but then you have them available if you need them in future.
The lab I have used is linked below.
https://www.vetdna.com/
I have been very impressed by their customer service who are knowledgeable about chickens and can advise you on what tests to do based on your chicken’s symptoms.
Now of course there is not much you can do about these viral respiratory diseases apart from supportive care, so you might not bother to do the swab. But if it matters to you to know what is going on I would go this route.