There are wayyy worse things than pot.

I smoked it as a teenager too, and guess what?
I didn't even have the "wrong crowd" of friends... it was just us good kids, with good grades, wanting to try something new.

And when I was done with HS, my experimenting phase was done too.

Its not always a big deal, so I would encourage you to actually LISTEN to your daughter's side of the story, ie, why does she smoke, where, who with and how often...

Then decide if her behaviour is actually worrying...