Frist I wanted to remind people that LOTS of people don't know the difference between a backyard breeder and a professional breeder. I'm not sure I did before I came here, and we rescue dogs. I just never thought about it. I just thought dogs either came from a pet store (bad), a breeder (someone who bred the dog -whether they were qualified to do so or not), or a shelter/rescue. I know the difference now, but I'm not sure my kids would.
Anyway, to the OP - good luck with your doggie! It sounds like you have more options than you first thought. I will mention this as well, and I hope it doesn't sound learless or cruel, just something to consider as a Plan B (or maybe Plan C or D). I have known many 3 legged dogs, and they not only have a good quality of life, but they didn't seem to realize they were disabled. They could run and jump like any other dog. If things don't work out, and the dog should lose her leg, it's not as horrible as it sounds. She can still live a long and happy life. I hope it doesn't come to that though, I just wanted to bring it up, just in case. I hope she is able to have the surgery she needs to fix her knee.