She was probably abused - verbally, physically, or both - by a male adult in the past. Give it time, she will learn that there's nothing to fear in him. I have several friends who went through the same thing with their shelter pups. Time, and extra effort on his part never to raise his voice near her, and to not, for the time being, make quick hand motions near her.

One of the most heart-wrenching scenes this reminds me of was my older brother's rescue Great Dane mix. She was not yet a year old, this big, "all legs" greature who had "only been beaten when she barked." Well of course my brother heard that, and had to bring her home. I met her after she had been with his family about a week. She had already been named "Princess" by my then 4-year-old (you probably guessed that) niece. The poor thing was sweet as can be, but underweight and terrified of anyone who wasn't my brother his wife or his daughter. I stood in the doorway of the kitchen, and she was all the way over on the other side of the room. I had been told about her past, so I crouched down and called to her quietly. She wagged her tail, slowly, then harder, but just could NOT bring herself to come any closer. It just about broke my heart. Princess did "sneak up on me" later in the visit, but I pretended not to notice her, so she could sniff me thoroughly without getting spooked.

A couple months later, she and my neice were tripping over each other to greet me at the door when I visited. It's amazing the difference a little time, and a whole lot of love, can make in a dog!