Puppy is afraid of men?

We adopted a lab/chow/border collie puppy from a shelter about two months ago. It seems to like women and all kids but does not like men. It likes myself because I was the one who got her at the shelter and loves my father. But she growls and barks at all other men. I've tried to hold the dog and have my brother come over to it but she still growls. Its petrified on my brother in law - she just hears his voice and runs. We are thinking about letting him take her for a walk.Any ideas on how to overcome this?