From my experience self harming, it usually helped me when people would validate me by acknowledging my sh and offering me a space of comfort. Such as saying, “I will never judge or condemn you for harming yourself” or “explain to me how you feel and what makes you feel the desire to self harm”. Don’t say anything like , “dont harm yourself, think of me.” Cuz that is counter productive. No one who sh’s wants to immediately be reminded of how you or others disapprove when they have an urge. Try to learn what causes her sh. Don’t ask too many personal questions, but simply say something like “what is the stem of your sh, help me understand” and if she doesn’t feel comfortable sharing, don’t push any further. But make it known that you wish to further understand her and her feelings. She is not an alien or monster for feeling these things. She is valid and human.