Absolutely, if you treat Anna and/or Eve like trash, there will be plenty of potential for drama. I even have plans to eventually allow you to manipulate the girls and turn them against one another.
One thing to keep in mind, Anna saw the Uncle do some truly terrible things to other slaves, even ones as young as Eve appears to be. And he told Anna all the time how he was going to do those same horrible things to Eve. She knew there was nothing she could do to stop it, that her sister was going to be raped and murdered, and there was nothing she could do about it. That knowledge ate away at her every day for years. To see her sister taken, even against her will, by someone who actually cares for her? Well, when compared to that was "supposed" to happen, it makes her happy to know her sister received better than that.