The fact that Brooke never destroyed those papers that Bill had drawn up while trying to trick Katie into believing he wanted to reconcile shows what a skank bitch she is. If she was truly sorry about fucking her sister's husband and getting knocked up, wanting to change, etc., she would have destroyed them. Why would she hold onto them? And now she's ready to pull the trigger on her sister, whom she tried so hard to convince she was changing and trying to become a better person, with them.
I really despise Brooke and no matter how many times she's tried to reinvent herself, she never truly stopped being the skank from the Valley.
I totally get that she wants to help her man recover his position at the top of the Spencer empire and have no problem with that, but to use papers he had drawn up as a ruse to trick and hurt her sister to achieve that goal is unforgivable.