Dysfunctional people use dysfunctional communication - including triangulation. As I mentioned, my husband talks regularly to his pastor and his parents about our marriage and tells them outright lies based on his 'feelings' at any given moment. Of course, they don't understand the dynamics of interacting with him, so they believe that he is telling them things that are factually accurate. He is more concerned about their perceptions of him than about me. His parents tell him to do things that have caused harm in our marriage - to get me under control. (more manipulation and guilting)
A one time lie or disobedience... .no. A long term unrepentant pattern... .perhaps. And... .really... .this church doesn't publish a "checklist" and they would not give a "blessing" to divorce.
Right, they wouldn't think that divorce is something that a "Christian" should do, unless there was an affair or something like that. And they wouldn't want to give "reasons" for divorce because that might make people think it was okay... .
For a lot of people in destructive marriages, the church can create a situation where they stay much longer than they should because they are concerned about church discipline and ostracization. Part of their journey is to examine it for themselves.
Another question: What would the consequences of her continued contact with her sister be?