Bullying may not have a gender but in the aggregate it's different between boys and girls. Note the word "aggregate". There are invariably anecdotes the contradict the aggregate view but the point is that it's not an absolute, just an aggregate.

There's lots of research on this topic.

You see the ripples of this well into adulthood. You see it as the expectations placed on girls and women where they're held to a higher standard than boys and men are. And who are the agents of that? Other girls and women.

I'm not female but all of my experience has been that no one tears women down more than other women and that female bullying is generally much, much worse than male bullying (at least until male bullying graduates into violence including sexual violence).

Why? Because it seems to be much more multi-faceted. Instead of being primarily physical dominance and signaling, it encompasses social alienation and psychological torment.