I don't thnk it was all that shocking when it occurs because there's plenty of foreshadowing that something's up between her and Hancock, though the way they actually went with it was surprising. Before the reveal, I kept thinking "she's one too - Hancock thinks he's alone but he's not. She knows where they come from. And he thinks he's a lousy hero but at least he's trying, she's just leading a normal life in hiding." A lot of the tension in the first half of the movie came from wondering what secrets she would reveal.