In other words, the trinity is an individual's favourite three pop girls out of a selection of the most successful or iconic female artists during a specific time period.

From an objective point of view, Lady Gaga would make sense in such a trinity seeing as her impact has been almost unrivaled this generation.
This is actually the first time I've actually taken the time to think about trinities even if they're talked about all the time on ATRL. It's actually one of the stupidest concepts I've ever heard about on a music forum.