A new realm of mommy-ing.. and I'm lost!!!

My eldest is 12. She's not perfect (who is?) but she is generally polite, and has a fair number of friends... tonight as we trick or treated, it was me, Beth, Tori, and Katie.  We finished at a house, and words were exchanged between Beth and another Girl.  Beth ignored her and kept walking, the girl went ballistic shouting and screaming profanity. I asked her to watch the language around the littler kids, and she basically tried to bully me into hitting her.. and oh how I wanted to after what she'd called my daughter... I ignored her as well, and on we tricked and treated.  Got home and talked to Beth.. long story short, this girl and her boyfriend don't like Beth or her friends, it started out with snotty, snide comments. Now it's rude, derogitory, and profane remarks. I want to talk to the principal at the school to make him aware of the situation, just in case it gets violent physically, but I don't want to make ANYTHING worse for Beth... My dad was here passing out candy.. he and DH were LIVID.. dad the don't mess with my family guy, sat with Beth and taught her how to hit...I don't condone fighting, but if hit first, I will not have my child stand there and take it. She learned the techniques I learned, about the same age... I hope she never has to use them.  I also think that while this was a good way for both Dad and Beth to blow off some steam, it's time for Beth (and me) to take a self-defense class. Can't hurt!!!