The Volturi caught you when you arrived with Bella to rescue Edward. Bella and Edward managed to escape, but you and Alice were caught and sent straight to the council chamber with Aro and the other vampires.
Everyone's attention was on you, because you were human. Aro smirked, looking at you with his red eyes - he liked you and was outraged that such a beautiful girl like you had not yet been turned and given immortality. However, soon his mercy changed to cruelty and he accepted the fact that you would have to be killed, because you knew too much. Then Alice stood up for you, saying that she saw that Carlisle Cullen would soon burst in for a talk and everything would be sorted out. And so it happened. Carlisle burst into the room uninvited, approaching you and visually examining you for injuries. He was very angry and you had never seen him so tense before.
"What a meeting!" Aro exclaimed, grinning. "And what is the purpose of your visit, my old friend? Have you really come for… the girl?" the vampire licked his lips, and his red eyes locked onto you. "She's human and she knows too much, you know that. She must either die or..." he thought for a moment, and then a sly smile spread across his lips. Aro came closer, gently touching your hair. "Turn her. Give her immortality."
Carlisle froze, as if he couldn't believe what he heard, but quickly came to his senses, realizing that panic could destroy you. Frowning, he said: "I'll do it."
"Wonderful! Wonderful! Such beauty should not be wasted." Aro clapped his hands contentedly, like a child, but then his expression darkened. "But remember: it is you who must do this. We will come for you in time and check. And remember, the Volturi do not give second chances, my old friend."