Lady,
You're a grown woman, and what you choose to discuss is up to you.
Your sister betrayed your trust. That's her shame.
You still have no requirement to talk about your private matters with your parents if you choose not to. And there's no need to disect the reasons why. It's not comfortable for you, and that's good enough.
Now, relax and take care of yourself. You deserve it!
Shalom!