Well, this may be a tough one... anyway, I believe there are two things to adress:
1) I have no doubt, looking at the several studies already made, that vaping is saf
ER than smoking... however, is it actually saf
E? Unlike smoking, we still lack long-term studies about vaping.
Starting a new addiction is very different from
switching to a safer one.
2) As we all know, cigarette addiction is so much more than simply a chemical one. (Just look at the 10% rate of sucess of the patch and gum). There's also the behavioural side to adress (That's the reason why e-cigarettes are so much effective, IMHO). So, even with zero nic, your daughter would still pick up an addiction. Only a
behavioural one, but still... why do it? If she suddenly picked the habit of chewing her plastic pens, would you encourage her?
And of course, there's the other side of the coin: I myself started smoking when I was fifteen...
on my parent's back, of course. My own daughter is also fifteen. She has seen me both smoking, and then vaping for the last four years. I explained to her that smoking is awful (and that's why I made the change, because I was unable to quit otherwise), but vaping is also
not to be taken lightly... it is just safer. Anyway, if she decided to pick an addiction on my back (We have all been fiteen-year olds, right?

), I would surely rather discover that she has been vaping, not smoking.
Just my 2 cents... as stated before, there's not an easy answer...