Yeah, you'd think Twilight would have remembered the day she met all her friends and fought a crazy moon-goddess and she herself concluded quite readily that the Elements were bodiless concepts, literally the friendship itself without any baubles, and they themselves were their avatars.
Writers: No, they're magic rocks from a crystal tree of love.
Discord: But the girls are the tree too.
Fluttershy: I'm OK with this!
Yeah, you'd think Twilight would have remembered the day she met all her friends and fought a crazy