In my first year of University I smoked A LOT of pot. I mean loads. Because that was what a lot of people do in their first year, Now though, rarely touch the stuff. Been a couple of years since I bought it myself. Every couple of months though I'll feel like "yeah, wouldn't mind kicking back with a spliff" and call up some mates to arrange a session. About as often as I feel like having some good quality whisky or wine. Its not about about an ADDICTION, its just sometimes a certain mood you get where you just wanna let yourself go loose. I think the people comparing it to particular foods (especially pie) have got the right idea. Most the time, not thinking about pie, but every so often yeah, would love a slice with vanilla ice cream on top.
Of course just like pie there are some stupid bastards who want it all the time, morning noon and night even though they're turning into fat bastards, or in this case just total stoners. Don't blame the weed for morons. Thats a universal concept.
Its less addictive than alcohol, FAR less dangerous than alcohol. Causes WAY less punchups, a lot less projectile vomiting, can be walked off far easier and gives a lot less aches the morning after. Still drink far more often than I smoke pot though. Not only cos I like my beer but just like pie, its kinda dull if you have it too often.
OP, think it wouldn't hurt to say you're cool with her doing it rather than giving her the stinkeye. Only get worried if she does it all the time. Then you might wanna suggest she cut it down a bit.