Madeleine Barrow is obviously Mare's sister, she's a middle child (Of course) she's basically invisible to her family to all but Mare. Madeleine is a half blood like her sister only her power is hydrokinesis (Look it UP) she doesn't discover it until Mare finds her name on the list meaning Maven is after her too. Dear Maddy doesn't even know she is this new blood she's just trying to live and survive hopping one day Mare will come back to her. Sorry if typossss.