Boy, that’s a tough one, my heart goes out to you. I’m not a vet, but if it was my little kid, I’d really have to think long and hard about a surgery. First off, they’re pretty stressful for the ferret. Second, you have to think about how long your little one has left, and if you would rather spend the time spoiling them. Our little guys usually only make it to about 7, but there are some people who have commented here that have them as old as ten. I guess what I’m trying to say is, if she was mine, I’d would probably not do the surgery, and just make her comfortable. It sounds like you’ve already gone through the treatment protocol, and have spoken to the vet. I’d contact another couple of vets to be sure, but at the end of the day you have to follow your heart.