Yep, oftentimes the Empire is divided into several eras. The Principate, the Roman Empire most people think of, is “Main Heroine but Thicc”.

“Frail Heroine” represents either the Dominate or the Western Roman Empire (itself a subset of the former).

The Principate was a mostly-functioning polity where the bureaucracy was light, and succession of the Emperor usually uncontested, with informal power-sharing with the Senate.

The Dominate was the post-Crisis of the Third Century Roman Empire, where tangled bureaucracy and despotic authority was the rule of the day, nearly every succession was contested, and the Senate was reduced to total irrelevance.

The Western Roman Empire is that period after 393 AD, when Emperor Theodosius I gave one half of the Empire to each of his sons. The two halves of the Roman Empire would remain seperate until the West fell in 476 AD.