Answer:
"Lady Macbeth did not kill Duncan herself because while he was lying there sleeping, he reminded her of her father. She says, "He could not mess 'em. Had he not resembled/my father as he slept. I had done 't" (2.2.1). Lady Macbeth says that she would have killed him, but because he looked like her father she was unable to. "
Step-by-step explanation:
Change wording.
(She could not kill the sleeping Duncan because in sleep he resembled her father. She expresses this reason in Act II, Scene ii, lines 12-13.)