Is she at a specialty hospital now? Her beat chance would be to let a nephrologist atteTpt to manage this. You might want to call the vet school in your state and see what they think.
Kidney transplantation can be done in dogs, but this case sounds much too severe, it's an uncommon procedure, and it would cost probably $10-$20K.
I am so very sorry.
There does come a time when the pain and suffering that a pup is going through is just too much with a very, very small chance of improving. And we are able (by veterinary medicine) to end that suffering. I know you want to do everything in your power to save her and you are a fantastic owner for it. Just remember to always be fair to her when making any decision to prolong her pain.