How will I get my friend to undergo drug addiction treatment?

She's so stubborn. She won't budge. She says heroin makes her happy and that I'm not a real friend because I'm trying to take away what makes her happy. What do I do? I don't know what to say to her, but I don't want to just give up and let her do whatever she wants because I know this is bad for her.

: http://alcoholdrugstreatment.info/how-will-i-get-my-friend-to-undergo-drug-addiction-treatment