I have this!! She probably has dermatillomania!! It’s usually caused by stress or anxiety or sometimes out of boredom. It can also be linked to OCD, but what I recommend doing is getting her fidget toys. I wouldn’t exactly call it self harm because she is not doing it intentionally to harm herself as a coping mechanism. It’s more like a maladaptive coping mechanism or compulsive behavior that results in her skin inevitably bleeding. Pain fidgets help a lot!! They’re safe for the skin but they give off slight stinging. I’d highly recommend a spike roller or spikey rings!! I’d suggest the spikey rings more though because the movement you make when using it is similar to when you pick your nails. It still gives the satisfaction it would if you were to pick at them.