It's horrible.
My DD is also 14, she's been assessed by CAMHS, who offered nothing because their opinion is that it is normal teenage angst with an inappropriate outlet rather than an underlying problem.
I don't disagree with that - but it leaves me a bit lost as what to do next.
DD thinks it's not that big a deal, her friends do it too and is really unwilling to engage in any form of help...I could pay for a counsellor and make her go - but if she's doing it unwillingly I'm not really sure what the point is 
The whole thing makes me so unhappy, I feel like I've completely failed her, a few months ago (before I found out) I'd have described her as a bright, chatty girl who I had a good relationship with...and if I didn't know she was cutting herself I still would.
It completely destroys me to think that my lovely DD is deliberately harming herself and I'm more used to it now than when I first found out, but, it isn't really any easier...sorry, that's probably not helpful.
There are lots of resources online about how to help, you knowing should make a difference - I think, although I don't know for sure that she's not doing it as much now I know.
But basically I'm posting to say, I think it's pretty normal to be upset, make sure you've got someone to cry at and hard as it is try not to do it in front of your DD because that just makes everything more pressured.