The vet agreed that there wasn't much quality of life left, so we he put her to sleep. It's not pleasant - she clearly noticed and didn't like the needle, but then it was all over. I've got this melting-pot of emotions in my head, on one hand its not something I wanted to do - to play god like that; but on the other hand would I want to live on in a mostly vegetative state? I dunno. The only plus I can think of is that it reminds me that I'm not the emotionless ice-sculpture I might sometimes think I am.
I had a quick chat with her remaining sister, who might have had a stroke or similar as she hardly uses her right front paw, and has issues with most of her right side, but at least she's up and relatively able.
The light that burns twice as bright burns half as long.