I think she's pretending to be innocent. I don't know why, but as far as her doting little broter-futaba-is aware she is innocent and tends to get taken advantage of.
Meanwhile, people like Minato, become as they because of people like her. I think that's what the point is here, or one of them.
meanwhile, Futaba is probably going to learn just how "good" his sister is, and how one should not judge a book by it's cover.
though not everyone is justified in what they have been doing. Still, I feel bad for minato...
forgot to mention if it was not obvious.
those are all the names of men, and it's implied that she is cheating on minato's brother.

The sister is a Psycho TOO!! Oh well why not....