I think that Shakespeare portrays her as a character somewhat in the middle of victim and predator.  One could call her a victim in that Shakespeare's Cleopatra truly cares for Antony and believes at the beginning that they will have a future together.

However, it cannot be denied, even in Shakespeare's version of history, that Cleopatra was a savvy politician.  She longed for attention and power and began with Julius Caesar in obtaining both.  While it seems like her relationship with Antony is more sincere, it is doubtful (as least from how Shakespeare characterizes her) that Cleopatra would have allowed herself to become romantically or politically attached to someone who could not benefit her own ambitions.