Hello, Alex. You're quite right; she couldn't have done anything. But, having been informed, I would have expected her to write it up in the Cabin Tech Log and/or mentioned it to the cockpit crew after landing. Then, someone like me would have fixed the snag! And, she obviously knew that the vents should operate better than they were and shouldn't have said that it was normal. It wasn't only my vent; several pax in other rows were fiddling with theirs.
Steve.