Are there any good stories out there that involve nightmare moon somehow being transported to another world other than equestria girls or our earth? Perhaps another version of equestria that different from one she originated from or another fantasy world all together?

Well, there is my story - https://www.fimfiction.net/story/436910/hoof-and-claw-versus-the-world Nightmare Moon is transported to our world, and she tries to conquer us.

Another story involving swapping worlds, in this case Luna and Nightmare Moon end up in Fallout 3’s DC.
https://www.fimfiction.net/story/137585/wandering-moon

It’s an older story but there’s also Tatsuro’s story as well:
There’s Nopony I’d Rather Be Then Me