Like I told chipsnopotatoes click the char:spoiler/robin iv/stephanie brown tag and read thru my series and you'll get a good idea of her history.
Of course, it's not positively certain Arthur's her bio daddy, but there was nothing to ever hint he's not, not to mention she looks a whole lot like him. A line in her debut was "All I inherited was his hair, birdboy," in response to Robin teasing her about her lame clues. And their hair is the same color and texture, not to mention similar skin tone and eyes. And he certainly acts like her bio daddy.