How do you stop caring about someone?

My friend is a real idiot. Drinks like a fish, smokes like a chimney, has god knows what flowing through her blood at any given time, has numerous ual partners. And generally gets herself into life-threatening situations a lot. She's been my friend for the longest time though, so it's not as easy as just walking away, but to be honest, I just want to prepare myself for the worst, she's not gonna last that long anyway. And no, I can't help her change her ways, she's too damn stubborn to listen. She is fun to talk to when she's not on something/someone though, so I'd rather just stop caring than stop talking to her