My Ruby is also a rescue, and she has gotten very comfortable with us, but can still be insecure. I know she would protect us from any animal, but not necessarily from a person. It seems to me that she is looking to me to protect her from people.
I don't know her history, just that when they didn't want her anymore, they dropped her off on the side of a country road. She stayed there, pacing about a 1/2 mile stretch of the road waiting for them to come back. She wouldn't come to anyone she didn't know, so the shelter finally set a trap to get her. When I got her she had tape worms and was skin and bones. She is still a lean dog, it's how she is built, but looks so healthy now. And the best thing? She is one happy dog. Her name should have been Joy!
For some reason it's hard to get a good picture of her. Whenever I try she sort of hangs her head and acts like she thinks I'm going to hurt her or something. We have never hurt her. She will always be a bit of a mystery.