Well, it's probably a hell of a lot healthier than drug abuse. She only has to worry about blood loss or infection. And hiding the scars.
With what she's been through and what she'll have to deal with for the rest of her life (and the extra shit she'll no doubt get from 'well-adjusted' people), I'd say cutting is something you should be least concerned about.

But since I've never had the urge to inflict (non-fatal) wounds on myself or know anyone who has, I recognize I'm most certainly not qualified to give advice here.
So I asked my good friend, Google.

http://helpguide.org/mental/self_injury.htm#helping
http://www.palace.net/llama/psych/ffriend.html
http://www.mirror-mirror.org/selfinj.htm