What about a Care credit card? Perhaps you can do that and make payments? Will the vet accept payments? Or another loan of some type? Is there anything you can sell? What about the rescue you work with?
I read a post where you said you would be willing to work in the vet office to help pay the bill...did you ask the vet about that?
Just trying to brainstorm....
When do you have to have the money by? Will you really have her euthanized if you can't raise the additional funds? Oh, I hope not....that just makes me so sad.
Really hoping things work out for her.