She's terrified at the thought that she's been killing and eating innocent people.
She lies to herself claiming "They were only rabbits!", but the reality of the situation is that they really were just rabbits!
As some of you might know, rabbits loose quite a shrill scream when threatened or pained, leading her to confusing them for human screams.
Its all part of the plight Orphan has to work through before she can come to accept what she's become and learn how to control her newfound terrifying strength.