In the very first episode we all hear the tale of the banishment of Nightmare Moon for a thousand years right? The part about the stars aiding in her escape?

Well I've been thinking... Princess Celestia was controlling the moon and stars for the millennium that Luna was gone right? I've come to think that Celestia had planned EVERYTHING that was to ever happen all the way up to season 3 (Except the changling invasion).

Since Celestia was controlling the stars, I think she purposefully released Luna at the prime time to allow Twilight and the rest to fulfill their roles as the elements.

Where was she during that time? Or even when Discord came back? Why did she send back the friendship letters at the perfect time? Seems too coincidental to me.

...this is nearly 100% guaranteed not true but it's a fanciful thought.