I'm with Hukuna on this one, it sounds too situational for my liking.
As far as Cleopatra goes, she's a difficult servant to make powerful because there isn't that much special about her.
If you want to keep going down that line then that's fine, but I looked into ninja culture to see if there are any notable names ('cause ninjas are badass).
1. Yamato Takeru. He's not really a ninja but he did murder some people, and got given a sword that can control wind magic.
2. Hattori Hanzo. He's a ninja/samurai kind of warrior, and one of the more famous ninjas. He's a master of spear fighting, but was also a clever general and reputed to have the powers of psychokinesis and precognition. (He could move stuff with his mind, and would have a huge rank in clairvoyance, a very useful thing for an assassin to have).
3. Mochizuki Chiyome. A woman descended from a clan of ninja. She started a school that took women from the streets and taught them how to be ninjas. Aside from having the skills herself, she would likely have somewhere between 200-300 weaker followers to gather information.
You don't have to use any of these if you want to come up with something for Cleopatra, but I thought you might appreciate the brainstorming.