I believe so many of us get taken in by female sociopaths/malignant narcissists because we are conditioned to think that all women are nurturing. That's what society tells us. We're bombarded with loving images of mothers hold their babies and women helping one another. However, there is a dark side that's rarely discussed. One out of every 25 people has a serious Cluster B personality disorder, in which they have little to no regard for others. Without this inner guidance, they have propensity to do a lot of damage. They not only don't care if they hurt someone else, but they appear to derive psychological pleasure from setting up scenarios in which others fall.
It's commonly said that most sociopaths are men, and that they outnumber female sociopaths by a margin of four to one. However, some experts also believe the number of women suffering from this disorder is vastly under reported. Women who harm others tend to do it discretely. They go after social relationships, and they don't leave a paper trail. Their actions are also, technically, not illegal. So they don't run into criminal implications as often as men do. Nonetheless, female predators are still exceptionally dangerous.
No doubt this is an area that needs a lot more research, so innocent parties know that female sociopaths do exist and they also know what to watch for, before a friendship with another woman moves past the acquaintance stage.