Well. I'll be honest. The whole time travel thing is new, but if you want to get technical... Starlight cannot alter her own timeline. Explanation is that if starlight hates the mane 6, she will eventually want to alter their history so that they never meet each other. Therefore bringing in the fact that if she changes the mane 6 never becoming friends, she will never meet them, want revenge, and likewise change their friendships. It's a paradox loop. Besides that, the second Starlight changed that from rainboom ever happening, twilight would have never found friends, become the princess of friendship, and she would have never been telling Starlight anything because she wouldn't have been there. :diamondtiara:
Point is, if Starlight changed any of the mane 6' past to not interfere with starlight, she would have never done it.