How to Communicate With Your Dog?

I recently adopted a Chesapeake Bay Retriever from the animal shelter. She is a great dog, but I can't seem to communicate with her. I've tried training her, but she doesn't want anything to do with me. The other dogs will push her out of the way to get the treats and she just wanders off. She doesn't even care for me to pet her. What is going on? How can I better communicate with her?