My dog barks at EVERYONE she doesn't know! ( er spaniel/shih tuz )?

My dog barks at everyone she sees until she gets to know them once she knows them shes really friendly (even the vet said that). When she barks at people im sure its scary because its a mean bark it sounds like shes ready to bite you! Im sure I could just introduce her to the neighbors and she'll stop barking at them but how do I get her to not bark aggressively at everyone we see on our walks?