The report from the Vet :

Maggie has a complete rupture of her right cranial cruciate ligament, and a torn right meniscus. Increased abduction angle in her right shoulder and stiffness in her left shoulder = medial shoulder instability on the right and has been overusing her left forelimb to compensate.

What it means:

Arthritis and bone degeneration in her right front shoulder, her left side is also hurting from arthritis and overusing it to keep the right from hurting so much. Then she ripped her knee out, so she is holding it off the ground and taking all of her weight on he remaining good leg and two painful front shoulders.

With a knee brace/harness, she will be able to walk using the bad rear leg - but it likely won't be normal, just usuable. The degeneration of her front shoulders means the arthritis is going to spread, so other joints will likely be affected in the future.

For the moment, we are going to get the brace. I cannot bear to have her put down if the brace will let her have a more normal life, and we'll do what needs doing to keep her quality of life high.

At some point her liver will fail or she will get a massive infection or some other catastrophic medical failure will occur, and at that point we will likely have to let her go. But not yet. :)