It might be worth looking online to get some specific advice about self-harm. I'm the first to admit I handled it all wrong when I first found out, got upset, went on to dd, removed all blades (this is a debatable thing, I've had differing advice on this) and so on. Now I follow the advice I've been given from her therapist and online, which is to accept (but not to like) that this is both an expression of distress and a coping method, treat it matter of factly (so 'you've got some bandages on your arms', would you like help with dressing that'), buy in dressings/antiseptic/sudocream so they can keep things clean. We have also done things to prevent, like distraction, having a nice memory box, therapy, anti-d's with varying levels of success. My dd didn't self-harm for about six months, but her ED flared in that time, make of that what you will, I have always felt the purging aspect of ED is similar in function to self-harm (plus it is actually a form of harm); it's a maladaptive habitual coping mechanism we want them to stop! She self-harms very occasionally now by scratching/scraping, so removing blades/scissors is not recommended by her therapist, but I have heard differing opinions on this (I would look at online advice from a reputable charity); CAMHS said remove. Even the experts don't agree.
So worrying, so stressful. We can talk about it now, I wouldn't say openly, but enough to be able to help if it happens again, which it occasionally does.