"I mean, it's there..." She can't see it? Maybe it's only visible from a certain angle? Now that she can see it, she figures it was probably warded in some way, but what's the trigger—

Hm.

She puts the candle down. The door disappears from her sight. She picks it back up again; the door reappears.

There's a couple more candles around; why they'd be at the counter is anyone's guess, although it seems to suggest something a little more complicated going on here. She hands one to Cassandra. "Here."