You don’t need anyone’s permission to no longer see your sister
Exactly. But I can see why she asked.
Even on this thread someone has called their relative nasty, a fantasist and a compulsive liar because she cut people out of her life. That may all be true in that particular case, but also, ime people don't easily accept it when people want to reduce contact with family, even if it is probably the best thing all round. And people can get nasty about it too, when it really isn't their business. Also important to remember that even siblings who for example cut out parents may have different memories of their upbringing. It's difficult to know from a outside perspective, even if you're a sibling, exactly what has gone on for that particular person. So best to accept it when people go no contact. Or you can always go no contact yourself if you truly believe they're a "nasty compulsive liar".
In my family, my sister called me neurotic, not normal, insane, crazy, a psycho, every time I disagreed with her or wouldn't let her have free access to my home. It's the main reason I'm low contact with her and because I did that, she has put it about that I am crazy. I'm not crazy / a fantasist or anything like it. I just don't like her and I have good reason. So I really object to the pp implying the op might be "like her relative" eg "a fantasist". People aren't automatically insane because you don't agree with them or they don't like you or someone else in your family. I'm sure that pp might be right about her own relative. I don't know her. But at the same time, going NC with someone doesn't automatically they are "unhinged" or mentally ill.
It's just interesting the language on this thread, as it does seem to be the commonly held view that someone going low or no contact with a sibling or parent means they must have something wrong with them mentally. That's so coercive and needs to be challenged.