Jack: Did you ever wanna be anything but a priest?
Father Benedetto: Have you ever wanted to be anything other than a photographer?
Jack: I do what I'm good at.
Pavel: And above all... don't make any friends, Jack. You used to know that.
Father Benedetto: I ask him to look after those of my friends who are sinners.
Jack: All men are sinners.
Father Benedetto: Some are greater sinners than others. But those who seek peace are much sinning in the history.
Father Benedetto: Of course... You're American. You think you can escape history. You live for the present.
Jack: I try to, Father.
Father Benedetto: All the sheep in my flock are dear to me. But some are dear the most. Especially those that have lost their way.
Answer: Because she didn't, but once she saw evidence of who/what he was, he had to kill her to protect his identity.