You need to try to figure out why she is behaving this way. She could be shy and she is frightened. she could feel that you are not the pack leader and she is trying to take over and protect you.
If it is shyness and a mistrust of strangers, then giving the strangers treats to give her might help, but my dogs will not take treats from strangers.
If she feels that you are not doing your job as pack leader than you need to establish with her that you are in charge.
Try this website, he has a lot of good information on that subject.
http://www.dogchannel.com/experts/cesar/default.aspx