My sister Lena’s friend regularly screamed at her, made fun of people, was ableist, etc.
She is on-and-off nice and mean. Right now, she’s nice. Before, she hated Lena. Now, she likes Lena. In a few months, she’ll hate Lena again.
Lena’s friend believes nothing is ever her fault and refuses to get help. She is very secretive and guarded, and acts very paranoid. Along with her defensive behavior, this makes me think she’s sadly being abused if she isn’t just a jerk.
She has quite the ego, but I’m not sure if it can be justified. Lena wants to be her friend and help her even with her behavior.
(She apparently has NPD)
You are free to dislike people and to choose who will be your friends, your sister also have this freedom, maybe you could offer help if things get too rough with Lena, and give advice if needed, helping people is not easy specially if Lena doesn’t accept it or want it.