Hun I think you really need to talk about risky behaviours and personal safety - excessive consumption of alcohol (among other things) can lead to all sorts of regrettable situations. And of course there's the issue of trust and responsibility as well - with her mother, but I"m pretty sure that'll be a conversation that is clouded by whatever other issues there are at home.

There are some good resources at this website: National Drugs Campaign. It might be worth having a bit of a read of their booklet to give you some ideas.