Why Does My Sister Get Away With Everything?
Every family quietly assigns roles, and nobody who gets a good one ever asks why. The rules land differently on the two of you because of: 1) role assignment, one kid gets reliable and one gets fragile, and the rules follow the label instead of the behavior 2) the fundamental attribution error inside the house, her mistakes get read as circumstances and yours get read as character 3) reinforcement, because the parent who avoids the louder fight teaches everybody exactly who is worth fighting. She is not getting away with anything. She was handed a different rulebook.
What is actually happening
Roles got handed out early
Her mistakes read as circumstances
Yours read as character
Being reliable became the punishment
Myth vs Reality
Myth
If you point out the double standard they will fix it
Reality
They know. The standard exists because it keeps the house quiet.
Ask which of you they call when something breaks. That is the whole rulebook.