They're all still competing for men, probably, although it's true that in general women can be "mean" to one another.
Once you're out in the real world and can make choices in terms of friends, it's much easier. Like attracts like from what I can see.
I've been in the same book club with the same twelve women (not all can make it to each monthly meeting) for twenty years. Over the years husbands have occasionally asked to join; I'm fine with it, but it's always voted down. They believe they wouldn't feel as free in discussing things. They're probably right. The meetings, especially once the "book discussion" is over, can be sad and hilarious, sometimes both at the same time, but men might not appreciate some of the stories and confidences very much.
Likewise, some of the best trips of my life have been taken with a group of my women friends. The six of us go somewhere at least twice a year. No drama, just lots of chat and lots of laughs, and no needy children or husbands to take care of...
Have you ever seen the movies Steel Magnolias? You ought to watch it. It's very funny.