I would caution anyone who is trying to understand cutting against making any sort of generalization at all beyond “they cut”. In my admittedly not-vast experience (but at the same time not confined to few people) with this, the one thing I have learned above anything else is that the reasons and practices behind cutting are as varied as (shocker here:)) the people.
Catalyst gain her trust … that’s, I think, the best advice I can give you. Pushing the issue may make her want to take to you about it–does she have a lot of people she can confide in? Does she know she can confide in you? Things to consider. However, it may also push her away from you because she may have had people try to intervene in the past. Back when I was engaging in similar practices (that never drew blood, but would have been seen by most as similar enough to warrant, to them, large amounts of attention and possible intervention), I didn’t want anyone’s help with it because I felt it was under control. Whether or not it was is another deal altogether (as well as why I no longer do it), but the people who found out about it were the people I could trust and who I knew wouldn’t push the issue if I told them not to because they knew how to help me.
It may well be that she was clumsy with an iron, in which case all this (for this particular instance) is needless. But if she is cutting, try to give her a sense that she can be safe and relax with you. More than anything else, I think, that’ll help her to deal with whatever issues she’s facing in other areas of her life.
Just for the sake of some level of education, here are a few reasons I’ve heard about why individuals cut:
They want to know if, at that particular time, they’re blocking (a practice in which you basically feel no emotion whatsoever). This is one big reason for what I was doing.
They feel the need to punish themselves.
They feel a deeper connection to … their inner self? when they cut.
What bobkitty said about trying to draw attention to themselves. I would probably have been cutting in HS but the support network I’d have needed for it to be “successful” wasn’t there at all. Dunno if that’s a good thing or not.
To cover up some other pain (mostly emotional/psychological).