good job for rescuing her! she sounds really cute we would love pics, of course!!

Aggression towards friendly strangers shouldn't be tolerated. It might start as barking, and could easily escalate to biting, or she might just be scared or nervous. Do you know how well the previous owner socialized her? She might not be used to getting walked, and approached by strange people. Just take it slow, have her associate people with positive things. Enroll her in obedience classes or practice diligently at home with at least one or two good obedience books... get her to do a solid sit, down, stay, wait, and settle. Have her sit when some one approaches wanting to pet her. If she barks, she should be told a stern NO or WRONG, move her into a sit and when she's quiet give her praise and a treat. Slowly start to have people offer her a treat in their hand, have them stand at a distance so she can approach them, not the other way around... then progress to letting people pet her once she's comfortable with taking treats, and eventually she'll hopefully realize that not all people are going to hurt her, or you. Also, ask people not to bend over her while they pet her, and ask them to pet her chin or cheek rather than patting her head (dogs tend to dislike getting patted on the head, its a dominance thing).

There are a lot of people who have better advice here... but I've used this with getting my dog used to neighborhood people. Sometimes dogs do bark at people, occasionally, when they feel a bad vibe from them but it shouldn't be tolerated all the time out in public. Good luck!!