Finally I remembered what I had forgotten.
I quickly returned under the gaze of Silvia and Lys to where I was sitting talking to Silvia and picked up Selene, whom I had left behind.
He had cast an anti-recognition spell on her, so unless someone was looking for her on purpose, no one would notice her presence.
I put her back on my arm and followed the rest. They, who paid special attention to my movements, noticed the weirdness and quickly the magic stopped affecting them, so they could notice Selene.
I mean, it's not like she did anything wrong, so it didn't matter if they looked at her. And while dark magic is frowned upon, it can be used.
A lot of artifacts like presence-reducing artifacts and such that use dark runes and the like to work. In fact, it doesn't even matter much if one has an affinity towards darkness, like Elena.