Because she's a dominant hermaphrodite with the social intelligence of a primate, that's why. Smithsonian magazine has up an amazing piece about spotted hyenas in Kenya, detailing their matriarchical clannish society and bizarre private parts (hyenas were long thought to have witch-like powers, including the ability to change gender at will to foil predators—in fact, female hyenas have extremely long "peniform" clitorises and bulbuous labia that look like testicles, and even scientists can't always tell the difference). Dominance is matrilineal, and literally passed down in the womb—dominant females release testosterone into their wombs during the final weeks of pregnancy, making their offspring, both male and female, more aggressive and more likely to consolidate power. Females eat first, gang up on insubordinate males, and bully potential mates for years until finally accepting courtship (insert stupid "just like college" joke here).
It's pretty fascinating to read about matriarchies in nature, given how rarely they occur among humans outside of myth and fantasy, both the horrific and the utopo-sexual. Of course, female hyenas dominate through testosterone and aggression, not through some sort of hippie-dippy communal love-in thing (what are they, bonobos?). So does that make it any less a matriarchy? It all comes back to the old "ruling like a woman" thing—such an untested and strange issue, especially now that it's apparently OK to call Hillary the candidate with "cojones." Spotted hyenas may be a more powerful metaphor these days than ever, really...
--Britt Peterson