About the whole Emperor thing: there was never any British emperor simply because the "Emperor" title [i.e. Kaiser] was bound to the continuation of the Roman Empire, which was the Holy Roman Empire [i.e. Germany], and abandoned after world war 1.
The Korean title would probably be DaeHwang ["great king" if translated to English], which just means the king has the complete sovereignty of Goryeo. We have a terminus post quem of 918 (the time the Korean Kingdom was established) and a terminus ante quem of 1897, which was the end of the kingdom of Joseon and the beginning of the "Korean Empire" under "Emperor" Gojong;
That is unless this story is a story about said "emperor" Gojong (at least his age would be fitting, he was about 22 years old when he began to strive for power officially[1873]).
However if this holds true, then he's been already married to her for over 7 years[since 1866].
It also means that her future looks grim, as she seems to be the later Myung-Sung[as she's his first wife],
who was assassinated in 1895, two years before Gojong would even become the emperor, leaving her at best with less than 20 years of life expectancy...