And the first girl who uses an indirect asymmetric attack? This approach will not work.
"... Teach your kid to fight back and fight smart. Protect the weak. Be hell and misery to bad people. ..."
There is a concept of proportional response and if you fail to apply it you could actually cause more damage to others and yourself. You do not want to "unleash the beast" inside. People are killed every day by someone loosing control and going too far. There are long term consequences for this type of approach. Consequences for yourself and others.
You have to decide before hand with a cool head what are your "rules of engagement?" Where do you draw the line? What is your proportional response? Is it offensive or purely defensive? Are your motives pure? Or are they to "do harm" to save face?
If you want to "fight smart" I'd advise Akido (合気道) because the core ideas are faithful to the ideals of "be good", "minimal harm" and self preservation. Akido allows you to achieve this through redirection of force and removing "ego" from the equation. You can use Akido techniques for both physical force and psychological protection.
Maybe these ideas are too subtle. But one thing I notice is the pattern of those being abused repeating the pattern of abusers. There are alternatives to break this cycle. Remember, "your actions have real consequences", short and long term. [0]
[0] Lynne Soraya, "Friends and Allies: What being bullied taught me about friendship" ~ http://www.psychologytoday.com/blog/aspergers-diary/200910/f...