Why Cleopatra was more likely killed by Octavian than suicided

Since Octavian planned to bring Cleopatra to Rome to display in his victory parade, it is unlikely he killed her. Being thwarted in that intention, he did have a statue of her with an asp curled around her upper arm displayed in his triumph. Antony and Cleopatra had lost everything. The son by Caesar was dead, and he was her great hope, even though as her marriage to Caesar was not recognized in Rome, a vain hope. In Rome, Octavian, childless Caesar's grand-nephew, had been adopted as his legal heir before the liaison with Cleopatra. Her kids by Antony (who were left out of this film), had no claims on any type of power or property. Alexander Helios, her eldest surviving son, twin of her daughter, Cleopatra Selene, (by Antony) would have been able to claim his mother's Egyptian throne, but with the defeat of Antony and Cleopatra, that was not possible, so none of the children had any claims anywhere, and as was Caesarion, were the children of a marriage that was not recognized in Rome, so did not even have claims as Antony's heirs Antony and Cleopatra were powerless to protect their children.
I don't think it was ever stated anywhere what Octavian's plans for Cleopatra were beyond exhibiting her in his triumph (which did not always happen immediately after the victorious imperator returned to Rome.) Vercingetorix, defeated chieftain of the Arverni, in the Galllic Wars, was held for 6 years in the Mammertine Prison until Julius Caesar's triumph, where he was paraded in chains, then strangled. It is unlikely that Octavian would have allowed Cleopatra to return to Egypt or retain any of her power, considering that he had murdered her son Caesarion, and she would have been vengeful. Her children by Antony, twins Alexander Helios and Cleopatra Selene and their younger bother Ptolemy Philadelphus were paraded laden so heavily with golden chains they could scarcely walk. They were then given into the care of Antony's Roman wife Octavia, sister of Octavian, (who must have been the pagan world's version of a saint.), and were raised by her. The two boys later disappeared from history, but Cleopatra Selene, granted a large dowry, was married to Juba II of Mauretania who had been brought to Rome after the defeat of Pompey with whom Juba I, his father, had allied himself, and paraded in Julius Caesar's triumph. Juba II, raised by Caesar, learned Latin and Greek, and became Romanized. He was granted Roman citizenship. After Caesar's death, Juba who had become friends with Octavian and accompanied him on military campaigns, notably Actium in 31 B.C., was granted a kingdom in Numidia. He,with Cleopatra's daughter at his side, became Rome's most loyal client king. Artifacts identified with them have been discovered.
So, although Caesar and his grand-nephew were revengeful toward conquered enemy leaders, that revenge did not extend to the offspring.

I could be a morning person if morning happened at noon.

I think that she committed suicide because she didn't want Octavian to use her as a symbol of how awesome he was.

Do you smell smoke?

Not a fact, but a legend. The fact is that Octavian claimed she, as well as her servants, died by snake bite in a suicide. The science to support this story is shaky in hindsight, but it certainly served its purpose in its time.