I am so sorry for your loss! How heart breaking. You did all you could and such is the circle of life as horrible as it is. My cat killed baby bunnies and mice and yet I loved him dearly, that dog was doing what it only knew to do...sadly.
I am so sorry for your loss, our pets are so dear to us. I hope you find some solace in knowing you tried to save her and that she was loved, which is more than many animals can possible know.