Nacreous
Fire trainer
First if we will be following her character in the games, her Pokemon will be strictly on the dragon side or perhaps anything that will be reptile-ish.
Second, if the writers want to market Pokabu they would give to Ash who has an already established starter and character. Iris herself is yet to establish her charactor, let alone Kibago. Giving her a starter would mean lack of apt screen time for Pokabu.
Third, let's remember that during the OP there was a time when Ash caught three Pokemon in three straight episodes anf this series is known for it's Kanto feel.
Lastly, I seriously doubt that they will let Iris challenge the gym because hypothetically let's say Ash will go only against Dento and Iris will go against Cornn who will go against the third brother who has Hiyappu.
So what if it has a Kanto feel?That doesn't mean it'll be a copy of the Kanto days.And those that say Best Wishes will be a rebirth of the series,well rebirth means starting again from scratch and doing things differently so with that logic I'd say Ash might catch different kinds of pkmn and not the usual Water,Grass,Fire trio