First of all, with Cleopatra, you will need to see the Ancient History syllabus to see what you can't do as you can't do anything that significantly overlaps the examinable syllabus and Cleopatra is an examinable personality.
I would probably not allow the topic due to the above criteria but...
You could assess the way she has been portrayed/viewed throughout history rather than just look at her within her own time. e.g. the way she is portrayed in Shakespeare and later fictional/filmic versions.