To answer this question from the outset we must consider that any Hollywood film's end goal is to entertain and make money and not to accurately represent historical fact. The vastly differing characterisations of Cleopatra throughout the decades seem to suggest that the era in which the film is made plays a big part in how she is portrayed as opposed to the Roman depictions of her.
The supposed speech by Octavian reconstructed by historian Cassius Dio although mostly focusing on Anthony's shortcomings as a leader also describes him as being 'bewitched by that accursed woman', a theme echoed in the 1917 portrayal of Cleopatra by Theda Barat. Her Cataclysmic influence over Anthony is highlighted in the film by the 'bewitching', vampish, dangerous, predatory and overpowering demeanour given to Cleopatra. Although this seems to mirror the portrait painted by Dio of a woman who 'enslaved' men (also demonstrated in Horace's Ode 'while the mad queen with her contaminated flock of men diseased by vice') it must be noted that only stills of this film remain so by and large we are basing the interpretation of the character portrayed by Barat solely on image rather than voice and the spoken word, which cannot be said to be an entirely accurate appraisal. Given that this film was made at the time of the Suffragette movement we cannot rule out that the portrayal of a dangerous woman stems from current events rather than historical sources. Newspapers and the media in 1917 were awash with stories of women using violence to gain a foothold in power so although the Theda Barat interpretation of Cleopatra rings true with many of the traits described by both Horace and Dio, you cannot rule out that the suffragette movement also had an impact in the way she was portrayed.
The 1934 Claudette Colbert version of Cleopatra (described as 'a comedy of modern manners in fancy dress' ) seems to be constructed completely as a product of the time rather than an accurate interpretation...