After reading all of the posts in this thread so far, I can see varying viewpoints with equal clarity. So my questions are:
What about doing cannabis is offensive to her?
Is it the drug, itself, or your reaction to it/what it does to you?
Or is it that she doesn't want to be around anyone who does substances?
Why is it that your going out with your buddies for beer, doesn't bother her, but your smoking cannabis, does?
Short version:
What is the root of her objection?