Having them in plain sight means the cards are bound to be seen, mentioned, occasionally touched. If the prospect of Mulder handling them bothered her she might have tucked them away, or explicitly told him to leave them be. That's not to say she would let just anyone play with them, but she thinks Missy wouldn't mind-- so who would she be to object?

"Be prepared for challenges, opposition to the things you've recently accomplished or gained," she rattles off idly, easily, like the cadence of something memorized by rote. Scaphoid, lunate, triquetrum, emperor, hierophant, lovers. "You could make that into an answer to nearly any question."