Why did Lady Macbeth kill herself?

Lady Macbeth once wore the "pants" in her marriage. She controlled and manipulated her husband with great skill. By the time Act 5 rolls around, Lady Macbeth is full of guilt, isolation, and paranoia. Really, she switches places with her husband when he felt these things earlier in the play. L. Macbeth has nobody to talk to. She can't purge her guilty conscience to anyone. Macbeth has long since left her n the dust: she no longer matters to him. So L. Macbeth walks around naked incriminating herself by muttering past deeds and lamenting that, "all the perfumes of Arabia will not sweeten this little hand."