there are a lot of posts like this.. you can search too on good things about weed, or something along those lines..
but i know where you are coming from..
Welcome to Jack Herer's Home on the Web
its been posted on this site thousands of times probably, but it is a very resourceful site which also has the book "the emperor wears no clothes" which you can read the entire thing online now.
just do some research from links givin in this site and put together some kind of fact sheet for her to read and talk to them about it, be serious in all means with them and dont let them think you do it "to get high"