Nowhere, Never
Nopony.

...

Wait why is somepony here?
It shouldn't have started, i wasn't ready

Twilight started to converse with someone whom she shouldn't be able to hear, uncovering truths she sould have never learned. And Celestia is definitely behind this.

How to react?

Isekai'd? not really.
A way to use my scraped idea for an AU? totally!