I do agree with others that I'd read a different spelling of "
Erin" as more unisex, but ultimately anyone of any gender can have a name and a nonbinary person can have any sort of name (like my name,
Cecil, is historically masculine). Good for your friend :) It's always nice to find a name that fits, even if
Erin tries out a few of them later on (I tried on a handful before going by
Cecil)