This sibling rivalry goes a little too deep. Barbara and Carol are the leaders of the D and C Blocks. We learn that they end up in max after plotting and successfully executing the murder of their younger sister.
The friction between the two sisters stemmed from a story from when they were teenagers. Each claiming to have ownership over the story, a feud ensued. Now, old dogs performing the same old tricks, the feud between the two blocks is still alive and well.
With the guards playing a round of fantasy league amongst the inmates, one guard brings Carol and Barb to face one another, in hopes of starting a fight between the two alphas. The plan fails, and sends the two crews out for blood. Both plot a war to be held on the kickball field, creating a distraction to give them an opportunity to sneak into the B Block and kill Frieda for betraying them years ago.
Their war fails to launch and their distrust for one another forces a deadly fight between the two sisters. Both take their final breaths on the hallway floor, Barb bleeding out from her wounds and Carol with a screwdriver to the back.