Breaking a bad friend's habits peacefully.

Hi y'all.

I have a very close friend, let's call her Genevieve. Genevieve and I don't talk as much now, but we still talk frequently, this is because we used to be a part of a friendship triangle per Se, with another girl, let's call her Beelzebub.

Beelzebub and I used to be very close until she became a very horrid person, she was nice but she became this perpetually grumpy, insulting, rude and promiscuous person. She started hanging around many drug users and many people who consume alcohol inappropriately. Don't get me wrong, I'm not against people using beneficial drugs and when it comes to marijuana people can do what the want as long as it doesn't affect/involve me, and I don't drink and don't intend to but hey if you wanna have a drink bash on.

But my friends and I, are fifteen. I have already told Beelzebub that I have no further interest in being her friend because of the way she treats people and the misery she has caused me. I heard that she went round to her boyfriend's house and they had sex four times both with and without protection, her mother forced her to go to a clinic and such.

However I'm not concerned about Genevieve. She seems to have picked up a phew habits from Beelzebub. She admitted to me that she smoked on the occasion and that she had a couple drinks with Beelzebub. I told her I wasn't angry at all or anything like that but that I am concerned and don't really approve of those actions at this age but that I can understand her curiosity in amongst Beelzebub's encouragement would inevitably lead to her trying a few potentially dangerous things.

I'm not the kind of person to turn up and be like, "stop doing this or I won't be your friend." I'm not that shallow, but I did make her grandmother a promise that I'd take care of her and keep her in line to stop her from doing stupid shit.

Is there a subtle, or less intrusive way of discouraging the bad things she could be getting herself into? I don't want to blackmail her or anything but I would hate to see something bad happen to her.