Now please no one get me wrong on this, I believe that Queen Lilliam was really, truly horrible, but I think that there were probably many things that impacted her bad decisions like NIghtwing. First, we know that she was from the poorest of the seven clans which probably drove her to do something to where she would have power to make herself rich. Also, she had nine other royal sisters. I can't remember even after reading the book twice, but I am pretty sure she was one of the youngest ones. This could have been sort of like a Prince Hans situation like in Frozen. Now please no one misunderstand me. I am not saying that anything that Queen Lilliam did was right, but I think that looking into her motives causes the things she did to make more sense.
Star grew up in a herd that he had friends in, and he felt somewhat safe in Sun Herd. Nightwing may haven't had a life like that, so maybe this caused him to become a destroyer?