Twilight's lifetime of magical study had readied her for her newfound powers as an Alicorn.
Her years in Ponyville had readied her for the newfound responsibilities she had as a princess.
Her numerous foes over those years had readied her for the new enemies she would make as a leader of Equestria.
But being an Alicorn means being immortal. And that means notice from the powers that be.
And nothing could have readied her for the affections of a god