My heart goes out to you. It is so hard to see your adult child in a seemingly unhealthy relationship. My young adult daughter was involved in a bad relationship, but she wouldn't or couldn't see it, and I struggled for many years to get her to "see the light." Boy, did she get upset when I used that phrase! She had to see things in her own good time---which was four long years. The more I pushed, the more she pulled away. When I just pulled back and disengaged, there was no need for her to be antagonistic. Maybe the same would be true for your DIL. Whatever your father does, you can't control, so he will have to make his own decisions. You are living by your principles and it's good to keep those boundaries in place. I think Still Learning's suggestion to send the postage and just be done with it was spot-on. I'd minimize contact and focus on the things that give you joy. My husband and I spent a lot more time listening to music, walking in the woods, and visiting other family members and friends --- people who enjoyed our company and nurtured us. We decided to not make DD and her BF the main story of our lives anymore and it made a big difference. We had to be ready to totally lose the relationship with DD in order to gain it back, ironically. I'd say don't give up your happiness for people you can't control. We can only control ourselves. All the best to you.