It's because women are "catty" to each other all the time...similar to how cats just hiss to those they don't like...with the "fight" part added
when it goes beyond just hissing....
I always believed it was because women scratch more.
I think I remember an article describing, in the 1800's, how women would shaplen thier nails or attach copper slithers to the nails so they could
rake out the eyes of the enemy.
Maybe because they bite, scratch and make the same noize that when cats fight? Also, saying cat fight is more politicly correct then saying pussy
fight. Just my thoughts