Simple, find all of the information found on this site and others (NORML ect.) print it out, gather your thoughts together, then calmly explain the reasons behind your use and let her read the info on the truth about cannabis... Take everything calmly, fill her in on reefer maddness of the 1930's and 70's, and on how the government was out to demonize the plant from the get go with bad scince and lies.

Show her that even though your a stoner, you haven't lost any of the mental power needed to come up with a solid argument for your rights...