I recently started yet another re-read of HPMoR, and noticed something I don't think has been discussed before.

In chapter 1, Petunia is talking about Lily making her pretty (which I believe she did using a potion of eagle's splendor with the blueberries replaced by Thestral blood), and says

And Lily would tell me no, and make up the most ridiculous excuses, like the world would end if she were nice to her sister, or a centaur told her not to - the most ridiculous things, and I hated her for it.

I used to think that Lily just wanted to protect Petunia from the danger and possibly other reasons. However, after hearing the prophesy in Chapter 89, I'm updating in favor of Lily telling the truth as she understood it. Centaurs are, after all, great at divination, especially astrology (tangent: I've never understood how that can be used for predicting the future on Earth, because it seems like anybody for the last several hundred years could have then, in a vague way, predicted the entire course of human history at least until the Space Age) and may be able to see this coming. Usually astrology isn't the precise, at least not in canon HP, but when it predicts the destruction of the "very stars in heaven", it may be more precise (and the centaurs may care more).