There the mysterious young man was, conveniently enough, lying right next to a bear that looked large enough to satisfy her cravings for some time. She had smelled him, to put it more accurately his blood, from miles away. The biggest surprise on finding the scene was how, well, innocent he looked. He wasn't the stereotypical macho or snobby hunter, although he certainly was a hunter of some sort of Appalachian animal, considering there was no other use for the rifle in his hand. In fact, the young man had thick dark hair and an almost round face. She realized that she liked his face. She was still vain enough to want him for herself, no matter that meant that he could never go back to his normal life. Of course, from the looks of that bear, if she did nothing, he wasn't going back to his normal life again in any case.
So for the moment, Rosalie decided to ignore any possible consequences of what she suspected was about to happen to the mysterious young man and concentrated on the bear to feed her hunger and keep him from mauling the young man in front of her. Expecting only a defenseless young woman, he had no idea what hit him when she attacked with a speed, strength, and teeth that would never be expected from such a small body. Before long, the bear was in pieces and Rosalie had a nice long drink of blood, although she knew by this point that her thirst would never be fully quenched. But it would have to do for now.
Trying to convince herself that she was doing what she had to save the unfortunate young man, she picked him up, only vaguely noticing how easy it was for her in her new form. The smell and the looks of him, though, were entirely too intoxicating. Especially with her heightened senses and hunger pangs, she was worried that once she got started, she might never stop.
Although death might be preferable to life in his new form if he survived.
Trying to convince herself that she was, in fact, choosing doing the selfless course of action, she started the miles towards where Carlisle would be. She wasn't as tempted to kill him and drink his blood as she had thought she might be after so many years of refusing to be alone with a human, particularly one who had done nothing to her. Maybe, just maybe, he would not feel that his fate was worse than death. And in that case, he would be grateful to her, even if she didn't deserve it. Even if he would have rather died than live forever in a form dangerous to humans and that most of them thought was only a myth.
And after that, maybe that appreciation could lead to something more. After all, the only thing worse than being trapped on Earth forever, would to be trapped on Earth forever alone. If it weren't for other vampires being around, she probably would have tried to kill herself multiple times by now, and it had only been a relatively few years since her transformation.
Although it couldn't have taken long at vampire speeds to reach Carlisle, it seemed to take forever. The temptation to drink the young's man's blood grew stronger all the time. It would have been so easy to quench her thirst and rationalize that he was better off dead.