Lady Macbeth would like nothing better than to kill Duncan, the Scottish king, and help along the prophecy that her own her husband will be crowned. She even calls upon the spirits to “unsex” her, to make her less than a woman so that she can do the deed, for she feels her womanly nature holding her back from it. She wants thicker blood and no compunction or remorse. She doesn't want to hesitate for a moment.
Yet Lady Macbeth knows that she personally will not be the one to kill Duncan. She is still a woman, and that is a job for a man, particularly for her husband. Of course, Lady Macbeth will have to stir him up. She will have to question his manhood to get him to take the necessary step. She will have to come very close to calling him a coward. She will have to threaten and cajole, to use her womanly wiles and to hint that unless Macbeth kills Duncan, he will be no more than a mere woman in her eyes.
Lady Macbeth does, of course, participate in the death of Duncan but only as an encourager and assistant. Direct violence is not the role of women; although again, Lady Macbeth wishes it were, for her spirit is violent enough to kill the king even though she believes her body lacks the strength.