she smoked pot, it's not like she went and f-cked the local football team. It's time to graduate DARE class and get over it. :rolleyes
Have a little compassion and don't hold her to higher standards than you hold yourself. People are not perfect, they make mistakes. In the scope of a relationship, this is very minor, really really minor. That's not to say that this couldn't lead to a pattern of behavior, she could easily go do something more detrimental, and then lie to you about it, but so could you.