The twelve demon emperors represented the interests of different demons. Naturally, there were a lot of internal conflicts both in open and below the table.
In order to maintain a united front, the twelve demon emperors would elect a 'Dark Lady of the Nine Heavens', just like the ancient twelve demon clans created by the Nuwa Clan in the legends.
Theoretically speaking, the Dark Lady of the Nine Heavens boasted the capability to communicate with the thirteen ancient demon clans as the spokesperson of the Pantheon of Demons. All important decisions had to be approved of by the Dark Lady of the Nine Heavens before they were announced to the demons.
The Dark Lady of the Nine Heavens was the equivalent to the Speaker of the Star Glory Federation.