Prior to Duncan’s murder, Lady Macbeth is all ambition, both for herself and her husband. Upon agreeing with Macbeth to kill Duncan, she goes in to place the daggers in Duncan’s chamber. She considers killing Duncan herself, but stops, claiming that Duncan looked like her father. We don’t know what either Duncan or her father look like. In any case, this marks the beginning of Lady Macbeth’s guilty conscious and her moral conflict, which Macbeth himself will also be faced with. She then literally (and figuratively) stains her hands with Duncan’s blood when she returns the daggers. She faints during the ensuing confusion when the murder is discovered. (I think this can be interpreted as voluntary or involuntary – as a result of her being overwhelmed by the events). Her guilty conscience and fear of being found out also cause her to jump at the screech of an owl.