What kind of sister is this?

[slobone]

I have some bad news for you: your sister is going to keep on being your sister for the rest of your life. You can dump friends who behave badly, but you're stuck with family members.

So don't do anything that will escalate the conflict. Best thing is to confront her, and tell her how upset you are by what she's doing. She may not even be aware how hurtful her actions are.

And be patient with her. Like I said, you're in this for the long haul...