I've been on the message boards a lot, and 95 of them say things like 'I want to kill Rosalie' or 'How could Rosalie be so mean?' But, have you ever considered her POV?
Imagine you were raised to believe that you were special. That you would get what you want, and no one would hurt you. You believe what these people tell you. You trust easily. You are told that Royce is what you want. You believe this, too. You also trust him, as you have everyone else, because you had no reason not to. And, in this life of being so...controlled, so trusting, to let people teach you what you want, you only want one thing of your own, one thing in the world: a loving family. You've always been given what you want; you have no reason to believe that you aren't going to get it. Again, you trust others for you happiness. This is a mistake. Your trust is thrown aside, your privacy violated. As you lay to die, your hope is lost; everything you have been taught is shown not to be true. You cannot trust anymore. So, when you are turned into a monster, your hope vanishes further. You are alone, untrusting, and violent. You no longer trust companions. You do things in a fit of rage, not pausing to think. You were never truly taught what you wanted, people always told you. Except for that one wish. The wish you still remember from you previous life. When you see a man lying on the ground, dying from being mauled by a bear, for the first time in years, you find something you want. When you turn this man into a monster, you don't know what to feel. Remorse? Pity? Happiness? Disgust? You feel all these things, and he comforts you. Now, you have half of your only, dying wish. But you will never have the other half. All because you trusted. When the human gets pregnant, she asks for your help. She wants children, who are you to stop her? You decide that, unlike the people you planted your trust in during your innocent, naive human years, you will help her get through this. She WILL get her dying wish. Because, you know, she is set to be transformed already. If something goes wrong, she still can be. But, you can't stand to have her feel the pain you still do because you didn't get your dying wish. So, you become a person she can trust. You help her.
Just think about it. Even she has a heart. She was just not taught the right things in life.
-Stephieyy