Prior to receiving Macbeth’s letter in Act 1, Scene V, we don’t know what Lady Macbeth has been thinking. In this letter, Macbeth reveals to his wife that he has been named Thane of Cawdor and that the weird sisters have claimed that he will become king. So, before she receives this letter, we can only speculate what she might be thinking. But, since she was so quick to seize this opportunity for power, by any means necessary, it is possible that she may have been looking for this opportunity for some time. Maybe Lady Macbeth was a bit bored with her life as the subservient wife of a loyal Thane. On the other hand, she may have been like Macbeth himself. She may have been a loyal subject with no thoughts of greed for power and that such thoughts only arose when the idea was placed into her head with the prophecy of the weird sisters.
So, what was she thinking while Macbeth was fighting for Duncan? She probably was hoping Macbeth wouldn’t die in battle. She hoped he would fight well. She may have fantasized about Macbeth rising among the ranks to a high point of authority. But that is all what she may think of him. Lady Macbeth is frequently described as conniving and power hungry. But she is also a strong female figure. That being said, I bet she was thinking of Macbeth and her own situation in life. In this same scene (Act 1, Scene V), she asks to be “unsexed” so she’d have the courage to do whatever it takes to get the crown. So, prior to receiving the letter, she may have entertained a thought like, “If I was a man, I would have more opportunities in life. Since I don’t, I will live out these dreams through my husband.”