Well it all depends on what kind of sister you got. if your sister is a bitch to you, then blackmail her ass, if she's a nice sister then either dont say anything or just tell her and be chill about it. If you decide to smoke with her just walk in her room drop a baggy full of weed and say "is that mine or yours?"

and yo Weeds is a pretty good show, you can watch it online just search for it