go to the bathroom and clean / wash the cut even if it hurts, get a bandaid or grap toilet paper or towels and apply pressure until bleeding slows plus tell an adult
yeah the weird crying posts after confronting her is very manipulative. i can understand the feeling like a bad friend, but if they’re making you feel this bad then maybe they’re not a good friend themself. the fact they aren’t changing the behavior is not friend like, especially after you told them why and how it’s wrong and that it makes YOU feel bad