Oh Robin how awful for you. I am so sorry, and I can only imagine the pain you are feeling right now. Just know that you did what was best for Peach, I know she is running around and enjoying her life at the Rainbow Bridge. You gave her the ability to have fun and be a puppy again, and she will be eternally grateful to you for that. She is watching over you, and I know you loved her very much.
I am so sorry for your loss.