Okay so just incase people are wondering why Zeta never 'Met' a big sister.
When Zeta was active with his little sisters, the big sister's were the first little sisters who matured and Ryan didn't know what to do with them. So to stabilize the sister's, he kept them hidden from the public eye.
He had Zeta stay there a couple hours every day so they could be calm and balanced like him.
When Zeta 'Died' and the Events of Bioshock 1 happened, Sofia captured the Big sister's, who aged slowly after hitting their teens. She then proceeded to
'Condition' them to become powerful weapons after she got hold of Zeta's blueprints and handed them to Gil Alexander.
Their are a total of 40 Big sisters across Rapture, but only 8 of the Original Big sisters who were with Zeta.
