5 months old is a puppy. she needs to be around all different kinds of people and rewarded for good behavior. She is probably trying to protect you from strangers by barking and growling.
Maybe puppy classess would help her become more propperly socialised and comfortable with other people.
My Suzi is 5 months old too. However, she has a completely different personality. Suzi loves people, and gives anyone lots of puppy kissess. It is interesting how different a Yorkie can be from each other.