The story of Cleopatra's death, as handed down to us by her conqueror, is that she killed herself by means of a poisonous snake. According to Suetonius, the stunned Octavian summoned snake charming Psylli to suck the poison from puncture wounds found on her arm. Later, she was depicted in a wax effigy during Octavian's triumph with an asp clutched to her breast and contemporary poets like Virgil also alluded to the snake as the instrument of her death.
It could be that they were all wrong. As Plutarch eventually admits, no one knows the truth of how Cleopatra died. Strabo may have actually been in in Alexandria at the time of her death, and he suggests that she may have put poison at the end of a needle. But none of the ancients seem to have favored the idea that she gulped down a poisonous mixture in the form of a drink, so modern claims that there was no cobra and that she drank a poison concoction must be eyed with at least a little healthy skepticism.
It's become fashionable to challenge the manner in which Cleopatra died and also to suggest that she may have been murdered or forced to suicide. It's even theorized that Octavian sent Dolabella to the queen with an elaborate story about how she'd be dragged through the streets of Rome for the express purpose of convincing her that killing herself was the only way to preserve her dignity.
Adherents to these theories point out that Octavian was a master propagandist who wanted to be rid of the queen and was willing to lie about how she died so as to ensure that he'd be held blameless. However, it seems that historians ought to base their conclusions upon more than a belief that Octavian was a liar.
A living Cleopatra was an enormous inconvenience to Octavian. He was undoubtedly better off with her dead than alive. However, it's equally true that there isn't a single ancient source that accuses Octavian of having killed the queen or having encouraged her to kill herself. In fact, Plutarch tells us that Cleopatra was researching painless forms of suicide long before Octavian stepped foot in Alexandria. Moreover, we're presented by an undisputed claim that when Cleopatra was first captured, she was already trying to kill herself with a knife. Even after she was disarmed by Gaius Proculeius, the queen thereupon stopped eating and allowed herself to succumb to illness until Octavian threatened her children. All of this happened before the much ballyhooed talk with Dolabella, and establishes a pattern of suicidal behavior.
Finally, there is the matter of Octavian trying to revive her. Certainly, Octavian was not above play-acting, but this would seem to fit the pattern of historical sources that tell us the queen's death came as a surprise to him.
Like Plutarch, I'll admit that no one knows the truth of how Cleopatra died. But the preponderance of the evidence still seems to be that she took her fate into her hands and ended her own life...quite possibly with the help of a venomous snake. And for purposes of a historical novelist, suicide by snake was good enough for Margaret George, so it's good enough for me!