She shows that she can remain in control and is the stronger one of the two, by not panicking and ordering Macbeth around. She tells him to ‘go carry (the daggers), and smear the sleepy grooms with blood’, and when he refuses she shows no remorse by taking the daggers herself.
There are various influences on Lady Macbeth, but the letter from Macbeth telling her about the witches and the prophecies has the most effect. The witches make her believe that it is possible for Macbeth to become king and Macbeth himself encourages her that she may be able to convince him to kill Duncan because when she asks him how long the king is staying at their castle, he replies ‘tomorrow, as he purposes’, which suggests to her that he has ambitions as well.
She also talks about ‘spirits that tend on mortal thoughts’, so she thinks about dark subjects and can’t help herself, because they are ‘spirits’ and she has no power over them.
Lady Macbeth may be disturbed because of a child. She mentions ‘giving suck’, which could mean that she had a child, and she talks about it when she is trying to convince Macbeth to kill Duncan. This suggests that she has unpleasant memories of her child and they may have unhinged her because she talks about ‘how tender ‘tis to love the babe that milks me – I would… have dashed the brains