Lady Macbeth feels a bit sad in my opinion because when she’s reading the letter from her husband because all that he is doing is talking about the witches instead of her because he came back from war and the least he could do is to say that he is fine and he wasn’t hurt or that they won the war but instead he says that He saw the witches and they said that he saw the witches and also they said he will become king what that means that lady Macbeth is slightly happy because she will become queen and she will have a higher status than anyone else also when she says the milk of human kindness means that he is to kind to people or he is merciful to them and when she says thane of cawdor she is slightly happy with macbeth because her status as the wife of a soldier called macbeth and also he is king Duncan’s cousin so since he’s became thane which also means lord of cawdor which will make her status go higher and she will be respected as a queen (or as close to queen status) that is why she will try everything in her might to make macbeth even if it means that she will tell macbeth to kill his own cousin the king