She also had hallucinations about seeing spots of blood everywhere and she specifically mentions Banquo and Lady MacDuff. She is sleepwalking at the moment, while her doctor and a gentlewoman are listening in:
For Lady MacDuff she spoke:
The Thane of Fife had a wife; where is she
now? What, will these hands ne'er be clean? No more o’ that, my lord, no more o’ that. You mar all with this starting
For Banquo on Scene 1 as well she was heard saying:
Wash your hands, put on your nightgown; look not so pale. I tell you yet again, Banquo's buried; he cannot come out on's grave.
After this, the doctor basically said that her type of insanity was beyond his practice and to put the Lady Macbeth to sleep because she was clearly ill.
Lady Macbeth is troubled by more than just the killing of Duncan in Act 5.1.
The imaginary blood on her hands directly refers back to the blood on Macbeth's hands immediately after he kills Duncan in Act 2.2. Macbeth obsesses over the blood, worrying that he will never be able to wash it off, and if he were, it would turn the ocean red. Lady Macbeth tells him that a little water will clear them of the deed they've just done. That is, a little water will wash off the blood and get rid of the evidence against them. Ironically, Lady Macbeth is the one suffering from guilt and seeing blood on her hands in Act 5.1. She is the one obsessing at this stage of the play.
The quip about the Thane of Fife having a wife, of course, refers directly to the murders of Macduff's family members in Act 4.2. Lady Macbeth did not plan those murders and did not, presumably, have any idea that what she started with her husband would lead to that kind of slaughter.
Lady Macbeth's mention of Banquo refers to Banquo's appearance at the feast as a ghost. Specifically, she recalls the words she told her husband about Banquo's inability to harm them, since he is dead. This reference reveals that it is not just guilt that is bothering Lady Macbeth. Her husband's guilty visions, as she interprets them, and his inability to follow her directions to act normally and not draw attention to his guilt, also bother Lady Macbeth here.
The whole situation has gotten out of hand and turned into chaos. Lady Macbeth got what she wanted, but it didn't turn out the way she planned.