Complex sentence: She was an illegitimate child, fathered by a man who was already married, so she was treated as an outcast during her entire childhood, and her aggressive personality did nothing to alleviate the situation.
Split into simpler sentences: She was an illegitimate child, fathered by a man who was already married. Therefore she was treated as an outcast during her entire childhood, and her aggressive personality did nothing to alleviate the situation.