Did I do the right thing?

[Sugar]

You're golden.

Imagine if something happened (and I'm sure you were doing just that), how sorry would you be? Your sister has a right to know your mother could be disclosing information about her in your father's direction. Especially if your mother has been specifically asked not to. I'm a mom; I'd want to know.

This is your mother's shame, not yours. She's just pissed you made her have to look it in the eye. And that's her problem.