In this scene, Lady Macbeth seems to have gone completely mad. Of course, it is only happening when she is asleep, but her sleepwalking seems to show that she is deeply troubled.
She keeps getting up and doing things like pretending to wash her hands -- sometimes for fifteen minutes straight. She talks about the "spot" and about blood. Clearly, she is feeling guilt over the murders.
The gentlewoman does not really speak her feelings, but I think she is afraid. She says she has heard something she shouldn't have. And she says she doesn't want to tell what she's heard because (the implication is) Lady Macbeth would know she had told. So I think she is afraid of her mistress.
Lady Macbeth loses her sanity totally by act 5. Her insanity is foregrounded in the first scene of the act in Macbeth.The gentlewoman serving Lady Macbeth feels simultaneously sympathy and a sense of bitterness to such heinous path Lady Macbeth along with Macbeth chose to achieve success.
In act 5, scene 1 of Macbeth, it is presented that Lady Macbeth has lost her senses, and suffers from sleepwalking. She seems to have also a mania regarding her feeling of having blood in her hands. In the beginning of the scene, it is evident through the conversations between the doctor and the maid that she is going through an intricate problem. As the actions proceed, it is clear that she does walk in sleep frequently. Not only that, she has lost senses and has been a sort of maniac since she tries to wash her hands rubbing them as if there was blood there. She has a psychological illusion that the blood of King Duncan is stuck to her hands. Her inner guilt and constant trepidation result in insanity. Because it is she who is the closest observer, confidante, and to many extents, a partner of the brutal tyrant Macbeth in his monstrous crimes. She has instigated him and knows what dreadful deeds Macbeth has done by now. And she also knows it well that: "What's done cannot be undone". In fact, now, there is an indication that she seems to find her surroundings a hell which is a dark place. Probably that is why she keeps "light by her continually".
Her abrupt speech like: "who would have thought the old man to have had so much blood in him" or "All the perfumes of Arabia couldn't make my little hand smell better" is not only meaningless lunatic utterance; rather, the feeling of her that the blood is irremovable and her constant rubbing to wash it away, are the symbolic expressions of her continuous mental agony and sense of guilt.
The gentlewoman is presented as a very loyal and good servant. When the doctor asks her to tell him about Lady Macbeth's behavior in detail, she defies to do so by saying loyally: "Neither to you nor any one, having no witness to confirm my speech ". She is sympathetic to her Lady and very orderly. But, at the same time, when the secret is disclosed, she is just wondered, and states her bitterness to such devilish deeds Lady Macbeth has done, witnessed and inspired. Her speech- "I would not have such a heart in my bosom for the dignity of the whole body", because she can understand that the heinous crimes Lady Macbeth witnessed or instigated, result in her present condition "where the heart is sorely charged". Definitely, the maid is very caring and a sensible woman.
Thus, Lady Macbeth's real character through her psychological state is nicely portrayed in this portion of the play. And, the loyal maid has acted as a auxiliary character to convey the implicit message of this particular scene.