In Shakespeare's Macbeth, Lady Macbeth is a woman in a dominant man's world. She is extremely ambitious and authoritative, and eager to make plans. At the opening of the play, she has a lot of influence over Macbeth. Her only object for her ambition is her husband, however, as was generally true for all women of that era. Any leading she does will have to come through his position in society.
She is, of course, also ruthless, and some might even say evil, although physically defeating a ruling monarch through assassination or battle is somewhat the norm in Shakespeare's day, not to mention 11th century Scotland.
She is also not quite so ruthless as she wishes to be, and not quite so ruthless as she first appears. She prays to her spirits to make her as ruthless as a male warrior (thus showing she has natural limits to her ruthlessness). Then she cannot bring herself to kill Duncan because he reminds her of her sleeping father. Finally, she mentally and emotionally breaks down after Banquo, Lady Macduff, and the Macduff children and household are all slaughtered. Those murders were not part of her original plan, and were more hideous than anything she could cope with.