Canon is unhelpful on whether Illyria's actually empathic or just really really pretentious at describing what she observes about people's bodies with her enhanced senses. The effect's much the same: the ability to pick up the general emotion someone's projecting, even if they're trying to hide it.

If your character's got good shields or a body so completely alien to Illyria that she'd have no idea what she was seeing, or any other reason under the sun to say "Suck it, you can't read my kid" just let me know here!