One other thing to remember is that when dogs reachs maturity (12-18 months) they will naturally become more protective.
As Ann said, they go thru these "fear" periods several times during thier lives. All you can do is work and play with them and continue to build thier self esteam. (Lots of "good dog" when they do things correctly and very little amounts of correction).
Set your dog up for seccess. When she is calm, praiser her. When she starts to get upset, move away from the stimulas and allow her to calm all the way down. Once she is calm again, praiser her again. (notice the circle here). The idea is to show her that its not her job to be upset and that you are in control of everything in her world.
I also find it helpful to carefully socialize dogs under direct supervision.
As for ppl approching you, you may just need to say, "My dog is in training so please ignore her and dont approch her.