The witches, through trickery and equivocation, plant the seeds of murder, and Lady Macbeth waters the seeds that helps them grow.
She more than convinces her husband, Macbeth, to kill the sleeping King Duncan (through her own mischievous brand of innuendo and tongue-lashing trickery), she even makes it easy for him to do so. She drugs the King's guards, leaves the door to the King's room open, and then lets Macbeth know (by ringing her little bell) when everything is ready for the deed to be done.
Lady Macbeth is, in legal terms, an accessory to murder.
After the murder, her role, in addition to being a very dissatisfied Queen of Scotland, is to try to calm and soothe her ever-more-edgy and sleepless husband. As successful as she was in prodding Macbeth and helping him do the murder, she is as unsuccessful in assuaging her husband's paranoiac fear and guilt-ridden, murderous intentions.
The queen is the catalyst for evil ploying for and then taking territory within Macbeth's heart. She is the one who prompts him to take active choices to fulfil his secret longings. The lust for power and domination seem to be more present in Lady Macbeth than even in her husband, but the fact remains that it is primarily Macbeth's choices which determine the course of events and not those of his wife, as evil as she may be.
Although this is a bit anachronistic to say so, in Freudian terms Lady Macbeth is the "id" (his basic instinct) within Macbeth which wrestles with and then wins over his "super-ego" (his conscience of right and wrong). In more recent psychoanalytical terms, she wields her influence to turn her already neurotic husband into a bona fide psychopath.
Lady Macbeth is the pusher in the her relationship with her husband Macbeth. She is that little voice in Macbeth's head that nags at him and twists his thoughts to fulfill her own objectives. When Macbeth wants to stop the plot to kill King Duncan she is the first to do what she can to change his mind. She even emasculates her own husband to get what she wants.
she plays an important role