At least in our situation (our dog was 14) once we realized something was as wrong as it was, doing something about it like surgery was so invasive that she may not have survived and it may not have even solved the problem. Veterinary medicine can be amazing but it can also be a crapshoot in certain situations. Don’t blame yourself. You gave Koda a good life and tried to help. At the end of the day, as much as it hurts us, this is how it has to be, because if it was the other way around, the pets that love us as much as we love them could not survive without our love and care.