The only thing that changed in nature with the rescue of Sandy, was to deprive a bird of lunch the next day. The upside was an ambassador from the wild to help us all learn about a species we have to live with and may be seriously mis-understood. And indirectly, more about our domestic dogs and ourselves. We are a part of nature and it's easy to argue that we make many mistakes with our "stewardship" of it. Learning more about a species that we attempt to control can only help in our decisions. No harm was done with Sandy's rescue and many have benefitted by learning about her. She chose to live and did her utmost to do so. We just gave her a little help. Based on how it all turned out, it's beyond ridiculous to suggest we should have let her freeze that night.
Maybe you can explain further what you mean by "let nature take it's course" and the benefits of that course with Sandy.