Apparently, the Elements trading hooves means Rainbow Dash is supposed to sit around and wait for them to fix everything. She found the map, though, so she's going, no matter who's with her.

Idea more than story, again. Inspired by a series here I tried to read a long while back. "Rainbow Dash flies West," I believe was the terse, intriguing description. I bounced off right at the start. It just didn't manage to hook me, for whatever reason, but that description still drew me. If I were to build something off of that alone, I'd probably start it with something like this.

Note: as per RyRy, a detective of unrivalled capability, the story I'm thinking of actually has her flying East.