It's not "Stockholm Syndrome,", rather layers of trauma informing outlook and response.
Abused, degraded and traded by a father (learning that violence and intimidation generates results and instills fear in one's rivals) into the hands of a serial domestic abuser/murderer subjected to sexual violence, psychological torment and assault. Told repeatedly she is nothing more than a tool to create and bring up her husband's property, all the while knowing she was a replacement for the woman her husband actually wanted.
The only reasonable way to survive would be to capitulate, harden ones shell, follow the abusers pattern of violence and rhetoric to attempt to engender relief, and use the violence she'd seen to successfully deployed against herself and others to assert some modicum of control in her life.
She's a classic (and well executed) example if a victim of generational Coercive and Controlling Behaviour.
One need only look at the younger couple that Roy "counsels" to see how hard it is for victims of domestic abuse to speak/stand for themselves, with "outs" regularly only available when a 3rd party intervenes to remove the controlling party.
Hugo - brilliantly layered season overall