Thénardiers were rather expert at sneaking in to places where they weren't meant to be. Éponine had spent a long time, back in their own time, learning how to remain unseen... perhaps that was what'd backfired on her when it came to Marius, but maybe that wasn't all so bad. What she had here was infinitely nicer.
As such, dropping down near-silently next to her brother and lightly smacking him on the back of the head was easy. She dropped down the backpack she'd brought, grinning. "You'll like what I've found. Ten points extra if you get it in the windows."