Depends on the context

Well, here's the story.
After we broke up we still talked, yes. I left the GSA (gay-straight alliance) at our school, cried that day. Since then I've noticed she'd stopped wearing makeup and the bags under her eyes growing darker. Told her that she was letting herself go. Yesterday I told her to go to sleep earlier (she was at an event and didn't get home til about 9:30, which is understandable) so the bags under her eyes would go away. This morning, texted her. She was going back to the second day of the event and then told me to stop telling her about her fading, because it was "fxcking me up". Told her I thought it was true, then she blocked me on Snap and Insta. Am I wrong? All I did was defend ny point.

Maybe you were a bit harsh about it or she just doesn't want to hear any kind of criticism from an ex

Well makeup normally covers dark circles so honesty you could just be seeing that. Also, I don't think anyone would appreciate being told "you're letting yourself go". If you told me that, I'd tell you to screw off as well. It's easy to see why she blocked you, you treated her like an arse. If you could have said something along the lines of "are you getting enough sleep you look tired" that would have been 10000% better over telling them "you've let yourself go". You didn't 'defend' a point. I'd say you are wrong.

Thanks y'all. I know I'm an ass, and was like that even when we were dating. That's probably the reason we didn't last long in the first place

This is just my opinion, but I think it’s good that you didn’t just ignore her lack of self-care.