Where it's illegal, it would be a law that a Catholic ought to obey. There's no moral need to break such a law.
But in itself, I'd guess it's probably not sinful in moderation. That's just my uninformed opinion, though.
As I said, though, Catholics have to obey the law of the land when that law is not telling us to do something immoral. And there's nothing immoral about not smoking marijuana!
I'm not sure where she lives, but its illegal in most of the States (except for "medical" reasons).
I would say that in moderation, like you said "one or two puffs" it wouldn't be a sin, per se, just like smoking a cigar or drinking a beer or a wine every now and then wouldn't be a sin -- BUT, I would not ever smoke any marijuana because I've seen some of my friends start by smoking it every now and then and I've seen their lives slowly degenerate. My friend use to be a good guitarist, but then he started doing drugs, just a little here and there which I think is fine, but then he started progressively increasing the amount of marijuana he smoked, and started doing other drugs like LSD and Ecstasy. He eventually was expelled from every school in the area, sold all his guitars for drugs and now doesn't care about anything but where he's going to get his next drug fix or where he's going to find some sex.
I might add that settings were marijuana is smoked (at parties, etc) usually are sinful and you shouldn't be there anyhow.
I think it all depends are your particular situation. I don't like people who say that smoking and drinking are bad all the time, etc and I think that smoking marijuana isn't that much worse than smoking a cigar -- but, smoking a cigarette or a cigar doesn't usually ruin your entire life, doing marijuana can. Drugs can destroy even the best people's lives -- eventually their lives are ruled by drugs, some may also engage in frequent illicit sex, but after a while the only thing important to them in drugs, they eventually despair and commit ѕυιcιdє or die homeless on the streets.
We are bound as Catholics to avoid all occasions of sin, so for this reason alone I recommend that you not smoke marijuana, or if you already do, then to abandon the practise.