Maybe at a time they existed, but then maybe they started to die off, or live in lands outside of Equestria. A lot of cities they have are named off of ours.
Kind of, their never was an episode dedicated just for her. She makes minor appearances in the episodes leading to Twilight becoming an alicorn, and a few others.
I know it will be in Fredbear's Family Diner, maybe a little like fnaf 1. Maybe it will be in someone's nightmare? Please feel free to post your thoughts!