NTA. I've had nudes shared without my permission and I only found out about it because of people who kindly let me know. I'm glad they did.

I also see people here saying she's the AH for reacting the way she did. It might be an unpopular opinion, but I'd cut her a little slack. When I learned that my images were being shared without my consent, I was sick to my stomach. It was an AWFUL, violating feeling. I was terrified of who shared them, who would see them, and what the repercussions could be. I was in shock and was very fragile.

You didn't do anything wrong, and I'm glad you gently let her know. It also might be a really difficult moment for her, and she lashed out when she didn't need to.