Hi, I'm sorry to hear that your daughter is self-harming but it is great that you want to help her and aren't invalidating her in any way.

I agree with the others that the self-harm is a symptom of other things so maybe you could ask he at some point if there is anything that is worrying her. I don't mean to alarm you but maybe she has got into a gang or something and it is scaring her. Also this may sound like I'm using the 'attention-seeking' reason here but as I see it it is a bit strange that your daughter actively wants you to find out about the cutting. Has your behaviour towards her changed any recently? Could she be feeling unloved or like you are ignoring her or are angry with her? She might be wanting you to take care of her. How is she doing in school? She might be having problems there, could she be being bullied? I don't know how much you talk with her but maybe you could try chatting with her about if there is anything wrong, and if she doesn't want to say anything you could keep it open by saying she can tell you anything at any time and you wouldn't get angry (or whatever), at least that would leave it open if she gets any worries in the future.