Kat I am SOOOO sorry to hear about little Marty.
I didn't realize you had a little paw in your family. I just can't imagine how you must feel.
The good thing is that Marty lived a long life! When you found her today, she knew you loved her and she knew you were trying to help her. She knew on the way to the vet that you loved her so much. She would never blame you for anything, that's the beauty of dogs. Marty doesn't hurt anymore, she isn't feeling any pain anymore. She is free now! Think of her that way, free of the injuries and free from all fear. She is loving you right now from where she is.
She will wait for you loyally at the bridge.
I am just so sorry you had to go through this. Please take care of yourself at this time. Sending you lots of love and hugs from GA.