[Aerilyn]

It would be unjust if Fantina didn't make an appearance somewhere in the games. In DPPt it's said that she's from "out of the country." She has a habit of speaking French, and seeing as there's a high chance that this new region is likely based off of France, it would make the most sense for her to appear.

The idea I have for her showing up would be to introduce the player to the return of an all new Pokémon Contests. If I remember correctly, Fantina didn't get into contests until arriving to Sinnoh. Perhaps she could come back to her home region in the wake of Pokémon Contests coming to her country for the first time.

Short version, Fantina should be there.