I had adopted a "breeder" who didn't know how to play,ate like someone was going to steal it. Maybe the one you adopted had to guard her food, so no one else would get it. She probably was never socialized, as far as speaking to her. She probably doesn't understand words-like they are a foreign language. It will take patience. Do you have other dogs? I would sit next to her, while she eats, and talk to her,just reassure her that all is okay.Don't pet while she is eating, until she learns to trust you, and relaxes. My dogs don't EVER growl or attempt to bite over foods, but they always eat like they are starved, though they get PLENTY! I sometimes would put your "newbie" on a leash,for "lessons" so when you call her(not shouting) you can pull her over to you, and give her a really good treat.(special for that..)and tell her how good she it! Practice that until she "gets" it. She basically has to be treated like a puppy, until she learns things. The first time my rescue went to the toybox and took a toy, was so exciting!! Patience and love is what she needs-she is in a new world!