Anyone who says that women can't be as violent, fucked up and vicious as men are is full of shit. It's simply that female aggression manifests itself differently. A boy in high school gets pissed off at another guy in high school. They end up having a blue behind the toilet block during recess. Sometimes that's the end of it. Sometimes it's not. A girl, however, will go about it very differently. She'll systematically destroy another girl's reputation, relationships and integrity over a long period of time, until that girl is completely ostracised by everyone, including the teachers. It's just words right? Not nearly as bad as getting beat up? Well, yes and no. On the one hand, no bruises or broken bones. On the other, seven years of being simultaneously a pariah and under constant surveillance will seriously fuck with anyone's head. Unfortunately, this can get even worse.
It's actually not uncommon for women, especially women in strongly patriarchal cultures (for example any of the Islamic ones, but it can be just about anywhere where women don't have much by way of autonomy) to manipulate and persuade their male relatives that another woman is lose, bad, a sinning whore that needs to be punished. The end result is that the woman whose reputation has been destroyed is at serious, genuine risk of violence and/or rape because according to everyone on the block, she's a raging slut that needs to be disciplined. It even happens in Western cultures, for example to the high school pariah.
Also, physical violence is more common than you'd think. However, instead of the full blown beating a boy might cop, with a girl it's usually (EDIT: But definitely not always, there are some terrifying and explosive bitches out there; for a ways I lived near a train station that if you saw a group of teenage Aboriginal girls loitoring there, you left and went to a different train station, because the gang queen had an improvised weapon made from a simple fork; the outer two tins were bent, the ones inside were sharpened. If you didn't hand over your money she'd stab you with it. The sharp middle tines went in easy, and the bent tines meant that it needed surgery to take it out, like a fucking fish hook) a long term campaign of 'minor' physical attacks, enough to bruise but not enough to make a proper complaint against them. Women also can be very pragmatic when it comes to violence. Instead of straight, meaningless but gratifying physical violence, they will often balance their need for sadism versus what they can gain by keeping their victims around. For example, they might abuse a child or someone disabled for shits and giggles, but they're careful not to let it go too far, otherwise their victim might die or authorities might intervene and remove that victim from their care, which means that the abuser will probably lose the carer's allowance/pension that they were receiving.
There are women who physically abuse their domestic partners, many more than you'd think, but you don't hear much about that at all. If it's a lesbian relationship, well, the LGBT has a very nasty habit of pretending that female perpetrated violence just doesn't exist. Some of the shit that gets swept under the carpet is full blown nightmare fuel. And if it's a woman abusing her male partner, well, there's a snowball's chance in hell he's going to be taken seriously when he tries to explain what's going on, and why he can't defend himself against someone who is technically supposed to be weaker than him, the poor bastard. And lets not get into the whole "mental abuse versus physical abuse" thing, that's some complicated shit right there.
Even at the extreme end of violence, female serial killers are very often inclined to murder those whose death would be profitable for them. They will poison someone for fun and profit as insurance fraud. There are, of course, many female serial killers who commit spectacularly violent and bloody murders for no other purpose for the fun of it, but overall, women are much more likely to have both an eye for satisfying their own sadistic urges and for topping up their bank accounts at the same time.
tl;dr
Women can be, and often are, just as violent as men, but manifest that violence in a completely different way.
