I guess it would depend on how the cat's skin is able to absorb it,
as long as your cat is not real ill, it may be worth a try,
but if your cat is pretty ill,
get the pill and be sure it gets into her system.
the circulation to the kidneys gets back to normal,
and then she can be tested for kidney funtion,
the high thyroid levels have also created a condition that makes the kidney function look better because all the extra blood flowing threw them,
then when the blood circulation gets back to normal, the kidneys need to be tested again,
I would worry about the medicine not being absorbed and not decreasing the thyroid function.
maybe worth having the Vet review the kidney function numbers with you,
Specific gravity has been high in mine,
creatine and one more I can't think of, but your Vet should know.