She is a child. You are her father. That means no matter what, you pour into her even if you get silence, even if you get rejected. You keep sending the cards even if you get no response. You call even if she says no every time. It doesn't matter if she refuses for the next five years, you do it anyway. It will be exhausting. It will hurt. And you are her father.

I'm sorry there's no way to get inside her head (I don't know how things are with your ex). Open communication. Family therapy.

You do the best you can with what you have. Commit yourself to being the best father you can be and not giving up. It sounds like you love her and are in a frustrating situation. Keep at it. Keep at it.