Self-Improvement
Ves never spoke about the fourth statue. He even commanded the Black Cats to delete all of the footage and reports about it in the internal database.
He wasn't able to delete the records on the fourth statue of the Lifers themselves, though.
It was a lot harder to keep his creation a secret when he made it in a busy place. Ves had created his four statues during a crisis when he was stuck in a metropolis on a highly-populated planet. He probably didn't have the luxury to ensure that he was able to maintain total secrecy.
Though most people still didn't know what this supposed fourth statue was capable of, Ketis was different.
She was not an ordinary Journeyman but also a swordmaster. That boosted her awareness and sensitivity towards the sort of creations that Ves had made to a greater level.
It also helped that she frequently collaborated with Ves on a number of mech design projects.