>>31528940She was begged to come back for Kukui's league, it's implied that he wouldn't start it unless she took up the offer.
Alola didn't have much a league to begin with, so it was sort of "rebooting" the positions of both Trial Captains and Kahuna alike since Kukui constantly reverred official Pokemon leagues, seeing them as a better measure of a trainer's potential than the Island Challenge if not more of an open door for representatives. Acerola was part of the Elite Four despite not being a Kahuna previously and Nanu was free to turn down the position at will since it wasn't bound to tradition or pissing off a semi-deity. Anyone who finishes the Island Challenge is considered the Island Champion but before Kukui's League, the position of Champion was little more than a title and really the "end" of the challenge.
Kukui thought Kahili in particular being one of many previous Island Champions who probably ended up in some mundane position or long left Alola would be a fine candidate to represent their first official Pokemon League since she was mostly touring to maintain a sense of competition.
