Invisible, your GD needs you, but she will not appreciate your efforts, and I would say that she CAN NOT appreciate them, until she's a grown up, maybe not until she's a mom. So in the meantime, you must not give up.
I have a suggestion for you that is currently helping my complete outlook on life. It's based on one of those internet jokes about "what men wish women knew", the line is "if I say something to you, and you can take it 2 ways, and one of those ways makes you cry, I MEANT the OTHER way".
I doubt that your GD sais those words to you about not knowing your son to *HURT* you, she said it because she heard it and she likely wanted to hear you refute it. What if you took it "the other way" and just said "HA! Of course I knew my son, who do you think brought him up, who do you think taught him to do *insert something here that he did with GD or that she admires*, who do you think helped him *whatever*? I knew that he was a good Daddy who thought the sun rose and set for his little *nickname for her*"
As for remembering him, I don't think it's up to HEr to ry and remember him. It's up to YOU to remind her. You don't need to "push" it all the time, but whenever something comes up, you talk about how he would be so proud of her, or how he did that when he was little. Just little anecdotes and funny stories.
But whatever you do, please don't give up on her. She's already been "abandoned" by her Dad, she's afraid that the people who love her might leave.