Quite apparently her lines were recorded between tutoring and recording - that her tutor was beside her when recording for the line. Her lines were uncharismatic and soulless, although credits had been given to her for the efforts of eliminating heavy accent.

And she was casted well. Karai is like her soldier counterpart in The Legend of Zu. As Wongsaurus said, I believe that was a right move for the actress to be casted in a kiddie movie; it helped promote/reinforce her Hollywood "A-list" status because doing voices for animation is considered an honourable job for many A-listers.

Watch TMNT, it's not your usual Saturday toon.