Here's a story for you that I think may help with your decision:
When I was young and single, I had a magnificent rescued dobie mix who was my best friend. Any time she met a new human friend of mine, she had a way of telling me very clearly what she thought of them -- most of my friends she loved. I vividly remember one occasion when she told me in clear terms she strongly dislike a couple who was over socializing (growling and barking at them in a way that was very uncharacteristic of this dog) -- I later learned they were unsavory characters I didn't want to know. Her instincts were spot on.
I learned to trust her after that. She did the same thing with guys I dated. She never had as strong a positive
reaction to any man she met that was quite as overwhelming as the way she greeted the man who became my husband -- she knew
from the second he walked in the door to pick me up for our first date that he was going to be her papa, and she couldn't wait for him
to know it. It's like she recognized him from another life. She was right about him too!
Mr. Magwart was then not a dog person as a young man, and he at first thought she was sweet but weird. I knew how right she was about him one Saturday a few months later when he stayed with her when I went to run errands and I found them sacked out napping happily together on the couch (with my dog lying on top of him). She taught him to be a dog person, and once he fell for her, he's been the doggiest-of-dog people. He loves
dogs now -- and it's all thanks to that little dobie mix who brought out an inner animal-lover he didn't know he had.
The point of all this is to suggest that perhaps you might consider trusting your dog.
If she's afraid
of this guy, ask yourself what she's picking up that you might be missing.