That's a tough one.
It really depends on your friend, and how well she would take something like that. Alot of people would be very offended, but sometimes, when you have an extremely close friend, they would take it as you were looking out for them, rather than an insult.
I would judge it by your friendship, how close you are, and how her personality is.
Just remember, sometimes it's better to have a mad friend, and help them, then have a great friend, and watch them hurt themselves.