The problem is reflexes. Your current reflex to being surprised is to inhale and stiffen up. If you change that response to one in which you respond with violence, you will end up injuring everyone that startles you. If you didn't kill her, you aren't trained to deal with surprise. This example alone should illustrate why training for surprises is impractical.
Prevention is the only remedy for surprise attack.
Everyone, even a karate god with super powers, is equally susceptible to being surprised and overwhelmed. That's why all smart villains use The Element of Surprise TM . A child of that size is incapable of disabling a large male adult, no matter the training that he may have received. The reason is that the larger, heavier adult can, thanks to his size, absorb more punishment than the child is capable of delivering no matter how optimized his abilities may be. Martial arts are not a secret weapon that can be employed to help the meek overpower the strong.