She said she was picked by the Emperor to oversee the technology when she joined the Dark Council, but we know before the Emperor's "death", the council never had such a person, the council member of technology is Darth Mekhis-Darth Hadra.

Or, maybe there is some scheme behind it?

The codex said she was picked by the hand, but it also mentioned she took the seat simply after Hadra's fall, so that's a bit different than what was said in the novel.

The Dark Council’s official keeper of all things technological, Darth Acina inherited her post after her predecessor Darth Hadra was killed by Republic heroes on Corellia. Acina was personally tasked by the Emperor’s Hand with guarding the Arcanum: a vast storehouse of Sith artifacts and devices deemed too powerful to destroy, but too dangerous for anything but research. Acina controls all access to the Arcanum facility, making her someone the rest of the Dark Council continually seeks to impress. None have discovered what garners Darth Acina’s approval–but all agree that to speak with her is always a pleasurable guessing game.

 

After the Emperor’s vanishing, Malgus’s betrayal and the rise of the Dread Masters, Darth Acina retreated into watchful seclusion with her apprentices at the Arcanum facility. This proved to be a tactical error, as one of her apprentices had secretly sworn loyalty to the Dread Masters and later organized an impressive raid of the station and its many dark wonders. Her position within the Dark Council has become precarious, forcing her to scramble out of arrogant isolation and curry favor with others.