So you guys are all totally right about Joan having a voice thing. She hears voices, but she also has tele something where she can send her thoughts into other people's minds.
The Magician P.180-Josh awakens to Sophies screams in the night and finds Joan holding her hand comforting her,
"He took a step toward the bed, but she [Joan] raised a finger to her lips and shook her head slightly, warning him not to say anything. The glow faded from her eyes. "Your sister is dreaming," Joan said though he wasn't sure wheter she had spoken aloud or if he was hearing her voice in his head."
The Magician P.181-Sophie is asleep and Josh doesn't understand how Joan expects to help Sophie when Sophie is not conscious,
"She's asleep...,"Josh began. "But I will still say them," the woman murmured. "And she will still hear me."
The Magician P.195-Joan is convincing Germain to teach Sophie Fire magic,
"Her lips didn't move, and yet everyone clearly heard her say, "Francis, you must do it."