settle a bet between me and my dad?

my dad is convinced we are not eligible to claim citizenship under Stag 5 because my Oma became a US citizen before his birth. I haven't found much online to suggest that the order of naturalization is a dealbreaker, but I'd love to know more. ancestry overview:

grandmother
- born in Germany 1928 in wedlock
- married American citizen 1947 (in Germany, I think?)
- emigrated 1948
- naturalized sometime between 1948 and 1957

father
- born 1957 in wedlock
- married 1982

me
- born 1984 in wedlock