Teruo's probably going to be super offended that Ginevra thought he was the mole thanks for the vote of confidence mum.

He might notice her disappearances, if we want? After the Deepsong starts he'll have been wanting to keep a closer eye on the Sirens in their school anyway, and even if he doesn't comment on it he might have noticed her disappearing for hours at a time (bc he's a massive hypocrite and does the same, but at least he's still around the island)