you was the daughter of the boogeyman. So you could go into the shadows and not be spotted at all, you could also see different kinds of shadows no one else could. And for that reason, Blackbeard - Hooks cruel father, took you on board as he knew you'd be useful to spy and get gold and other things for him without anyone else seeing you.

The other part was though, for you to be treated highly and be respected, you was then married to Hook. Blackbeard forced it upon you both. You & Hook wasnt very fond of eachother at first, but things changed after an accident occurred.