The phrase “She did right by you” means:
She treated you fairly, kindly, or honorably.
She acted in your best interest or did something good for you.
Examples:
"Even though she had to leave, she did right by you in the end."
She made a good or respectful decision regarding you.
"He always tries to do right by his friends."
He treats his friends well and fairly.
It's a common expression in conversational English, often meaning someone fulfilled their moral or emotional responsibility toward someone else.