This isn’t just a “cry” for help. It’s a huge shout! She has let you see her arms. She wrote a monologue she knew you would read. It’s important not to dismiss what teens say as just a “bid for attention.” It is a bid for attention. It needs to be taken seriously. She has already cut herself deeply once. Whether by accident or on purpose, she could go too deep again and perhaps kill herself.
I hope there is a counselor associated with the school. You can’t (and shouldn’t) take this on by yourself. You don’t have the training to help her. But you can be someone who takes her seriously and who pulls in the appropriate assistance. Do what you can to get her to a counselor. Find out if there is a hotline or adolescent help line in your area and give her that information too.
Teachers are often the first to notice when a teen is in real distress. If the family is unstable, a teacher may be the only adult in a kid’s life who can provide some direction and support. I hope you will hold onto your empathy for such students. In my mind, providing some compassion and concrete help is just as important as correcting their grammar.
One caution: Sometimes kids like this are so needy they mistake good intentions to provide help as personal interest. If you speak to her alone, make sure your door is open or ask another concerned teacher to join you for the conversation.
I wish you well.