Don't let your hurt drag you into a parental alienation. Not sure if that's the exact term, it's when one parent tries to alienate the other from a child.
Is there a problem if D17 wants to see her mother? D17 knows the kind of reaction she'll get from you, that's why she didn't tell you. You need to gain her trust and respect back.
I have not read all the pages in your thread, I don't have children, so I can be totally off base here, but I would make sure your D17 knows you will support her wish to keep her R with her mother.
