A female friend-with-benefits with whom one shares such a close bond that there is almost a blood-relation.
Me and Shannon's like peas and carrots, but since we're not related she's only my KentuckySister, so I still get to stick it in her ass whenever I want.
Bosses you around and runs the family. Throw temper tantrums, needs to be treated like a princess, domineering, and doesn't hesitate to use manipulation. Her brother takes on husband duties and she may act like his wife.