I saw that, so I think I am not explaining myself well.
I can see how that might persuade Hanners to "do whatever Beatrice tells her" (although I think it's more likely that what would actually happen is that she'd call in Station).
But the issue is that Hanners has cut off ties. That is, their relationship has been destroyed.
This action might persuade Hanners to resume communication, but it would permanently destroy their relationship. Thus, it would be an entirely self-defeating move on Beatrice's part.
That is what I am trying to say.
I can see what you are saying about abusive parents, but I don't think that what you've suggest is the method she would choose. Some form of emotional blackmail would, in my opinion, be more likely, if she was to try anything and if she were in fact abusive.
But in fact, I see Beatrice more as a grossly neglectful parent, even though the effect is that of abuse. Thus, I don't think she would reach for emotional blackmail either.
I think Beatrice was blindsided because she honestly had no idea of the seriousness of the effect her actions were having on Hannelore. Thus, her reaction is exactly what I expected.
Am I explaining myself better?