Thanks for all of your kind comments.
Little Girl died of heart failure, the same thing that got her brother. Evidently the medications were enough to give her a few more months, but not the years that the vets and I had wished for. She did get one more summer of hunting mice and chasing leaves.
I found her on Saturday afternoon in the backyard. It was a beautiful warm fall day, and she died with the sun in her fur and the grass under her paws.
Her neighborhood kitty friends all came to pay their respects on Sunday, and I am not even kidding. I had a backyard full of cats.
Goodbye, honey. You'll be forever young.