Hi again, and thanks for waiting.
If no chest x-rays were taken, Izzy may have bronchitis, asthma or pneumonia. The cortisone shot will help reduce inflammation, but if she has a viral or bacterial infection, she will need antibiotics, as well. Here is more information:
For the moment you can run a humidifier in the rooms where she spends the most time and I'm glad you changed litter to a more appropriate one for allergies and senior cats.
I do believe it would be beneficial for her to be evaluated by the vet, again, and if it hasn't yet been done, imaging will show more. If money is tight, you can take her to a VCA Animal Hospital, where they offer a downloadable coupon for a first visit for new patients. Of course, you would have to pay for medications or any testing/imaging, but at least the exam will not cost you anything. VCA is nationwide, so I hope there's one near you. Here is the link for the coupon:
You can also apply for Care Credit, which is accepted at most vet offices:
I hope all will be well with Izzy and please let me know how she's doing. Thanks!
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