Then what you should've done is told her "too late, I already dumped it/sold it/smoked it/whatever" Then either hide it somewhere where you can pick it up later, let a bud hold it, smoke it, go home and then just tune out her bitching. Sorry your mom's so depressed, but really, I would just tell her myself. As long as you don't have any paraphanalia (which you don't anymore) or green on you or in your room then if she calls the cops, there's nothing you can do. That's how I would've handled the situation. And no, don't fucking punch her in the face, just tell her to fuck off, and then walk away.