Hate to hijack the thread, but I have to say something about this.Great question, my adult chihuahua does this. She does not like people trespassing in her space (our home). What we do is on spot correction whether it be a stern "NO" or something like water from a spray bottle. This seems to curb the occurence but can't say it does away with it completely. Good luck and do post if you find a fail proof way to correct the behavior.
Yelling (which is what CAPS is related to on the internet) or spraying your dog with water is most likely going to make your dog dislike strangers even more.
Welcome to the wonderful world of chihuahuas, where strangers are a nono, and kids are even worse. Many chihuahuas are easily upset, and something like a spray bottle is probably going to make her associate discomfort with the people, not with the growing/nipping.