Since you are over 18, your parents are in their 40/50s, so Granny is about my age- have you ever thought about the fact that your Granny lived through the 60s and 70s- hippies, peace, love and pot and all that jazz? She might be more receptive than you think! And if there is a medical reason......
Mine were SUPER religious people who think sin of everything "impure", but I don't blame em' with the world now-a-days....But she is naive to cannabis. She got a little porcelain piece of two Jamaicans with Rastafarian hats and the dreads w/ joints in their mouths. They are carrying a wooden crate with marijuana leaves (fan leaves) painted all over the crate and says smoking right on the side of the box/crate. It looks like it supposed to be a little stoner stash thing. She got it cause she thought it was "cute" LoL I cracked up when I saw it and asked if she even knew the meaning behind it! :wtf: Good Stuff!!