Your sister is a bossy spoiled entitled person. That is who she is as a person and you can’t change that. The best thing you can do is disconnect and don’t bother saying anything to her because engaging these toxic types with poor selfish character is a total waste of time. Engaging this type of selfish person only enables them to spew their toxic crap.

Toxic people don’t care how nice you are so blaming yourself when they behave in bad character is not healthy for you. These people can’t be nice so there is nothing you can do, and these kind of people actually prefer to get others to react badly so they can play the victim. They genuinely only have two behaviors, bad person and victim that’s the totality of their social skill set.