Okay, I have a theory about why Diane might be working with BadCoop. If we are assuming that Richard is Audrey's son, the product of BadCoop raping Audrey in the hospital, and if it is correct, as many assume, that BadCoop also raped Diane, then might Diane not also have a child? What if that child is Linda? And what if BadCoop somehow uses threats against Linda as a way to control Diane? To me, that would clear up why Diane is horrified by BadCoop but why she might do things for him. Also, it would provide a balance Richard. Maybe, somehow, This hypothetical Linda is the opposite of Richard, a very nice, pure young woman.