It’s typically a defense mechanism in response to organizational biases about female characteristics and an understanding that higher level positions are limited or capped out for woman. Therefore they go out of their way to distance themselves from other woman so as to not be labeled with those prejudices and because they are fighting with other woman for a scarce resource in the company: the very few upper management positions open to them.
So in North Korea’s case, the sister could likely be pretty damn ruthless.