I too wanted to say how sorry to hear of your loss. 13 years, I would give you an A+ for giving her a long, wonderful and loving life. I have never had a dog live that long.
Please do not doubt yourself that you could have done more or sooner or better. You did what you thought was right for your girl, and you did!
Rest gently now sweet girl, no pain when you are across The Bridge playing in the beautiful meadows with our pups.