Well, I'm not really sure what a ninja is. All I know is that Ninja Turtles is a cartoon that I was majorly confused by as a kid--I saw it a grand total of two times and didn't like it--never made sense to me. I think ninjas fight? But I'm not sure how.
But as for Pom Pom, I'm assuming she's a cheerleader who has no other name. And if you call her a giant balloon, I'm going to say she's a fat cheerleader. And if ninja and turtle go together, maybe she's one of them, since turtles usually aren't skinny like most cheerleaders.
So I leave you with this analogy question...fill in the blank:
Rob : Bob :: Robert : _______