Hello and welcome. This is just a short note to introduce myself or to request needed information for your problem. My name is ***** ***** I have been in the dog field for 25 years. I am a Therapy Dog & AKC Evaluator/trainer/ as well as an assistance/service dog trainer, specializing in behavior. It will be my pleasure to help you today.
Dogs bark for many reasons and the most general reason is because they have a fear issue. It is a dogs way of telling others to stay away from it. This behavior works for them because most of the time they are barking at something that was going to be moving away from them anyway, such as the person walking down the street. They do not realize this person was going to keep walking anyway, they think that their barking made the person move. So in that respect they are rewarded instantly for the behavior.
To change this it is good to put a leave it command in place so that when the dog starts barking you can give that. Leave it should mean take your mind off of everything else and put your focus back on the owner awaiting the next command.
You would also use this in conjunction with the heel command when on walks.
Also keep in mind that you have only had her 3 days, so that there is nothing at this point that is consistent in her life to make her feel secure. Rescues can take up to a year in a new home before they learn the house routines and the neighborhood routines which change with each season.
Try some positive obedience training such as clicker training to take her mind off of what is going on outside and have her focus on you. Training sessions can be very brief throughout the day. When she begins to bark at someone turn that into a training lesson by calling her to you, asking for a sit or down and rewarding that behavior. The more you can show her behaviors you want from her in certain situations and reward those behaviors the more she is likely to repeat them making undesired behaviors less over time.
I am going to direct you to links for clicker training in case you are not familiar with it.
Clicker training/positive method training/ print off
video’s to see how clicker training is done, scroll down to videos http://www.clickertrainusa.com/clicker-training-videos.htm
clicker maintaining focus http://www.clickertraining.com/files/auto-eye-contact.pdf