India: United We Stand

I’m so tired of my sister. She is 21 years old. In her masters. Does not have an iota of an idea how to treat our mother. Treats her like a servant. My mother lets her treat her like that too. Verbal abuses, disrespectful communication (on the lines of I wish you die, I wish your mom (grandmother) dies and you don’t get to see her body etc in the crass-iest language you can imagine). Every time pulls off a full drama about how she hates her food and ends up eating the most out of it. Has spit into her food when she was on her fast, slapped her multiple times, thrown her food, abused her, only for my mother to go back to her like a servant again. My mother has no self respect. My sister has never earned a single penny and the way she treats stuff I or my father have bought from hard earned money is pathetic, to say the least; never lived outside the house; wants everything served to her on a platter. And no, she isn’t like this with everyone. With her friends she is one scary cat. Her whole demeanour changes which is fake af. My father and I don’t interfere now because there’s no point. Anyway if I ever point something out, suddenly the topic turns to how I am a bad person. While I’m practising detachment for my own sanity, she’s my mother, it feels bad sometimes.

Edit1: As suggested by one kind stranger, I should have mentioned about her childhood trauma. She has gone through bullying by the hands of her friends due to which there are solid self esteem issues. Apart from that, she thinks that my extended family only cares about me (1st girld child on father's side; 1st child on mother's side) and she admittedly feels jealous because of the love and affection I got.

Edit2: Thank you for the comments people. I would first like to clarify that I am her elder sister and not brother. The kind of suggestions that people have put here, marrying her off, "selling her", calling her a slut, hardcore violence etc are not only bullshit but shows how the people posting such things themselves need help. Unlike pointed out by some people, no, Im not using my goddamn sister for some cheap clout here. I only wanted to understand different perspectives. Thank you to the people who tried understanding and painting a holistic picture, I have well noted such healthy, rational advices.