One could argue that pot and alcohol are not much different in terms of the "hard core drug" factor. BUT, like it or not, the thing that weed has against it is your girl is going to HAVE to deal with shady people to get it because as corny as it sounds, its illegal.
IMO, thats the red flag when it comes to girls smoking, they don't have the power to say, "you know what, its not important enough to me to have to run around like a shady b*tch trying to get it, just so i can get high, i'll just have a glass of wine if i want to unwind."
This is not that important when you're young, after all i wouldnt expect a 22 yo girl to think like that, and thats fine, but do you really want the mother of your kids or your grown a$$ wife running out to meet her hook up?