Well, if I remember right, her primary partner was a Haxorus. So I'd say mix it up and go with the Tyrantum.

As for regions. . . Well, it'd be interesting to get maybe get some more insight into her nature and/or origins (or at least a hint or two). First thing that came to mind was that maybe something from Ultra Space or the Distortion Realm could've been involved, so I'd say either Alola or Sinnoh, depending on which you considered more plausible.

I scraped most of it because of lack of time and interest.
I think I'll have something but more likely just have vore with little plot.