Damn, that does suck. You're right, you would think that being honest would make her take it a bit easy on you.. but Parents can be assholes sometimes. Just explain to her your reasoning (i'd pull up info on marijuana to back you up) and just try to get her to understand. It's one thing if you do it in her house, since it is her house and her rules should apply, but whatever you do outside that house should be your own choice. Good luck though... being in that position is never fun.