Poison one can of "the resource" with a mild sedative and put it in an obvious place your sister will check. When she comes to take it, tell her its poisoned. If she is the average human, she will guess you are being sarcastic. When she wakes up from the sedative she will tell your parents. This is where you can add "i told her it was poison". She wont take anymore... trust me.
If that doesn't work, your sister is a zombie. Take her out.
Ok, now seriously. Place six samples of "the resource" in your school backpack, and throw the pack into the back of your closet. Parents most likely wont go so far as to examine the inside. When the six cans are diminished, restock. Enjoy.