Well, I've got my old grey kitty an appointment with the Thyroid specialists to make her radioactive on the 23rd. The good thing about this is it is a cure! The bad thing is, it is expensive as in $925 flat fee, but that includes however long she needs to stay there and if they have to do a followup treatment. I'll still have to get her bloodwork after that at the vet, but it will be worth it to not have to give her twice daily pills and the cat lifespan is generally longer with this than the daily medication to treat her. Also, she doesn't easily take pills, so twice per day would not be a great quality of life for her considering that she has another option.
Anyhow, a decision has been made, a credit card will be used, and soon she'll hopefully be back to normal thyroid function.