Longshot, But I'm Searching for an Estranged Relative

I am searching for my aunt, who is German. I know very little about her, I don't even have a name. Long story short, I don't speak to my father's side of the family because they are terrible people. However, my paternal grandfather was stationed in Germany with the American military in the 1960s and had an affair, resulting in a child. I can't go to them for any help in finding her, and I'm not even sure if she'd be interested in talking to her long-lost niece, but I have always been curious. How would I even begin to search for such a needle in a haystack? I don't know if his name is on her birth certificate, or how to search for such documents in Germany.

If know a woman whose father was a scumbag American serviceman in the 1960s who abandoned her to go back to his other family in Arkansas, please message me.