it took me a long time (almost ten years) to accept my sister was a narcissist. She used to be my best friend. Some people get lost in their pain, in her case, she was being emotionally abused by my mother for too long. Maybe if you talk to your sister and offer help you’ll be able to understand her better. But if she doesn’t accept help there’s nothing you can do. My sister ended up doing really crazy stuff to destroy my life, I became her target. I’m still wishing I had stopped talking to her earlier.