She is not visibly Diabolin - the mod-notion was that she'd be wearing a cloak as part of her Eidolon costume that (magically) shrouds her body in shadows, but an illusion is also acceptable.
Other options:
no subject
She is not visibly Diabolin - the mod-notion was that she'd be wearing a cloak as part of her Eidolon costume that (magically) shrouds her body in shadows, but an illusion is also acceptable.