Self harm is scary, and especially when the person is so young. But it doesn't necessarily mean they are at increased risk of suicide. Of course, there is always the risk that the person may accidentally cut harder or deeper and unintentionally themselves serious harm.
However self-harm isn't suicide, nor is it a manipulative "cry for help". It is a way of managing overwhelming distress and emotional pain, and people do it because it works - at least in the short term. The physiological response to pain and harm is so good at grabbing our attention at a basic physical level it tends to get rid of, at least for a while, other distress. However the price paid is one of shame, regret and of course physical harm and frequently lifelong scars.
It's also true that in the longer term if people come to rely on harmful ways of managing distress they don't learn other, more effective tools.
Back to your question. We can safely assume she is distressed, and has some things going on in her life she doesn't know how to handle.
I'd invite her over and have a gentle, non-blaming, concerned conversation. Let her know you are aware of her recent self harm and you're concerned, and want to help - and importantly won't do or say anything to anyone without her okay. But that it's also important that she tell someone, so she can get some support and help with whatever is going on for her.
Lay out the options for her. Is there a school counsellor, or a teacher she feels comfortable talking to? Would she benefit from calling a helpline as a first point of call? Or would she like you to talk to her parents on her behalf?
If she refuses to seek out help, you will need to intervene with or without her permission, so you should tell her that. But that is the option of last resort, ideally, she can be supported to make that choice herself.
Because it's okay to know you need help, and at the same time - especially at her age - not know what help looks like. And even though it's hard we should certainly trust young people to know what help they DON'T want.