Let me preface that I have no problem with people who occassionally smoke pot...<quoted text>
As I see it, she has two reasons not to like it:
1) bad experience with a pot-smoking person, like a parent or sibling.
2) on principal, because she heard it's "bad".
If her reason is 1, then Amy can't help her. That's something she has to work out for herself.
If her reason is 2, then she needs to evaluate the actual situation and know that most people do not see pot-smoking as all that harmful.
It really sounds like she's standing on some principal that reality has shown might not be as important as she originally thought.
But maybe she's just the type of person who wants to be with someone that is sober and "present" 100% of the time. I can understand that, though it wouldn't bother me so much if it wasn't an every day thing (just as I wouldn't want someone that had to drink beer every day). It's just that she has to make that decision as to what she can tolerate.