Oh my goodness. You have been through so much with Sadie. First off, never feel badly about posting a question about a non-GSD. I love that this board is welcoming and informative to all dog owners.
I am in no position to answer questions about your girl's health. She probably does need to be seen by a specialist. I am never one to tell anybody to put a dog to sleep. But...You do need to look at Sadie's quality of life. There is a point, when enough is enough. I can't tell you when that point will be with Sadie. I can say that if you are able to get a diagnosis, you will need to think about her prognosis and the impact on her quality of life. To me, a continual decline, in quality of life, would indicate it was time to let go.
You have gone above and beyond for Sadie. Kudos to you for taking such good care of her. Please keep us updated.
Natty Boh 6-27-12
Annie 1998 - 8-2-12 RIP