Could this also translate as "She is American"?
Kind of. There is another way of saying that, but you could use this to mean that.
Ni allaf sillafu America ! (Why can't you guys spell it like we do in Welsh, which is how Americans spell it?) You can't change everything: we tried and failed before Gaidhlig became fashionable! Languages need to be flexible...
There are three different spellings for America - Aimearaga/Aimeireagaidh/Ameireaga
I have two dictionaries.
The spelling in Robertson & MacDonald's dictionary is Ameireaga.