I was a little disaponted with this quest as you don't actually fight Siren in this quest just trash mobs that are being controlled by Siren.

to my understanding Siren is a Primal.

when i heard that Siren was going to be in FFXIV i was hoping for a fight like Ifrit, Titan or Garuda

if I was to take a guess she would be summoned by the Lamiae? (yes I know this beastmen tribe is not in the game at the moment)