So if Sona is silent

Telepathic communication with Summoner

She can be heard by the Summoner. "Only you can hear me, Summoner".

Only you (in-game) can hear here because of some mental connection. More details in the old lore, but you can justify it currently as some mental connection (after all, you are controlling the champion without actually being them).

I mean, Sona's entire voice-over has been ret-conned out of making sense. So. But it was a psychic link between you and her.

I can hear her, she got picked on the opposite team.