It all depends if she has good lower body strength then something like kick boking or upper body strength then any one of a number of karate prgrammes. Their are also special self defence classes for women check your local council or maybe doctors for details.
Do you not think that us fellas know of such tactics sddsddean :) A 'box' is part of the kit for a door man or thug on a saturday night. I think you would have to have a bit more of a plan than just kicking somebody down bellow.