Lady Macbeth is not involved in the plot to kill Banquo and his son Fleance. This can be seen by referring to Act 3, Scene 3, where she asks her husband, "What's to be done?" and he tells her, "Be innocent of the knowledge, dearest chuck, / Till thou applaud the deed." There is no doubt that she shares her husband's concerns about Banquo and Fleance because she doesn't want Banquo's heirs to be kings of Scotland any more than Macbeth does. But her only complicity is suggested when he tells her, "O, full of scorpions is my mind, dear wife! / Thou know'st that Banquo and his Fleance lives" and she replies, "But in them nature's copy's not eterne." (Act 3, Scene 3) Evidently she means that they can be disposed of, but she makes no specific suggestions as to how it might be accomplished.
The murderers in Act 3, Scene 1, are undoubtedly victims of an unfair society, as are most lower-class men and women in a feudal system. But they are not necessarily victims of Banquo, although Macbeth manages to turn their pent-up hatred against him.
In Macbeth, both Macbeth and Lady Macbeth have visions of their own grandeur. Macbeth is excited by the thought of, not only being Thane of Cawdor, but, as the witches suggest, king. He ponders to himself that:
"if good, why do i yield to that suggestion Whose horrid image doth unfix my hair And make my seated heart knock at my ribs Against the use of nature."(I.iii. 134-137)
Even without Lady Macbeth's involvement, Macbeth is already having the most evil thoughts. However, he does almost come to his senses when he considers Duncan's position and decides that "We will proceed no further in this business," (I.vii.32), recognizing that his "vaulting ambition...o'er leaps itself."(27) Lady Macbeth, upon hearing of his apparent change of heart, manipulates him as she undermines him and insults his manhood: When you durst do it, then you were a man."(49) Even after murdering Duncan, Macbeth is confused and conflicted, desperate to "wash this blood Clean from my hand..."(II.ii.60-61). Lady Macbeth has to step in and return the daggers before Macbeth is exposed and they are caught out.
Lady Macbeth has had her own ideas of removing Duncan, having decided to seize the opportunity, as he visits her home. She will relish, "the fatal entrance of Duncan Under my battlements."( I.v.36) She then prepares herself, wanting to be sure that nothing "will shake my fell purpose," (43) and is prepared to go to any length, even suggesting that the spirits "take my milk for gall,"(45) to ensure that she can complete the task. She recognizes Macbeth's fears and reassures him that he can "leave the rest to me."(69) However, she is not complicit in Banquo's murder. It is interesting to note that Macbeth talks with Banquo moments before the daggers appear before him and he is reminded of the witches' promise to Banquo.
Macbeth, in his delusionary state, having killed Duncan, imagines that he "hath murdered sleep," (II.ii.43) and, in his frenzy, he has now also killed Duncan's aids. His killing spree has begun. He is, however, aware that he can use this information to his advantage, apologizing - "I do repent me of my fury," (II.iii.104)- in an attempt to hide his evil deeds. This reveals that he is far more cunning and purposeful than Lady Macbeth may have realized. She will still support him and will be required to make excuses for his strange behavior at the feast but, she has no idea of his plans. She encourages him to accept "What's done is done,"(III.ii.12) and tells him to stop fretting over Banquo. She does become aware that he has a plan to remove Banquo from the situation but remains, "innocent of the knowledge."(44)