She needs to be taught some amount of common sense. Even if you hate the police, you don't kick them. Contrary to the popular belief, a five year old can and will adhere to the rules of logic.

Edit: In this particular instance, I don't think that discipline is going to do much good, because the childs mother obviously doesn't know how to raise her child. If you don't know how to raise your kid, no matter how much you hit them or ground them or spank them, nothing is going to come out of it. Discipline is a learning experience. If you can't teach your kids, you might as well just give up now.