How do I convince my girl to let me smoke weed ?

Well... The problem is was that I was smoking with my friends without telling her,and I felt bad about it so I told her what was happening. We had our discussion and she forgived me but before all this happened she tried it her first time with me and my friends but it was my third time doing it. She liked it and said she wanted to keep doing it I told her we could but not at a regular bases more like once every 2 or 3 weeks she agreed with that. But she never did it again after that cause she never had the chance which over time then led onto her thinking it's bad only for pot heads, bums, losers,and bad guys etc.... And I mean queen Victoria in 1891 was prescribed weed to relieve menstrual cramps,Henry ford used hemp for his model t also it ran on hemp ethanol thinking green don't you think lol? And 172 countries are growing marijuana crops, in 1484 the pope declares that smoking cannabis is sacriligious, and now marijuana is 36billion dollar cash crop for united states, I mean in my own opinion if states are in the process of making it legal than why is it seen as bad? I mean alcohol is so much worse,and ciggaretes? I mean I see my mom and dad smoke it all the time and it's horrible I tried it and never wanted to do it again. Well I don't know I'm posting this question as in what should I do? And also yes I respect my girlfriends thoughts, she's her own person she can accept to whatever she wants it's her own body I agree with that. And amost forgot to mention she can't play games cause of the motions which is part of epilepsy she gets headaches,throws up and feels horrible. I prayed to God she doesn't have it, and I believe marijuana helps with epilepsy as well I mean what more can you ask from this plant? It's a superb plant.it grows straight from the Earth. My birthday is coming up soon and I want to do it on my birthday only with her. Well tell me on what you think I should do. Thanks.