I wish you and your friend nothing but the very best! Unfortunately there are two factors here to consider. The reality of this matter is heroin is by far the best and most addicting drug there is and here in the States at least is dirt cheap. The other factor here is your friends age, 18. She is still very young, and heroin addicts can remain addicted longer then any other drug. Some for decades! But it only takes one over dose to end that run. And I agree with others who have said she can only stop if she wants to. Treatment is useless unless the person is actually committed to breaking the addiction. She will want to stop, and the hard fact is most simply do not want to stop. My suggestion is to continue to be her friend but accept that you are powerless to change her out come. She is in control of that. So do not get dragged in to this too deeply. All you can do is be there as a friend when she needs one. Continue to tell her how you feel, just remember this could be a very long ride. Good Luck!