I think it's fine.
Fiona is common enough that I wouldn't think twice if someone wasn't Irish or Scottish. At least if they're caucasian because you can't really tell what they are or aren't from looking at them. I love
Fiona too.
Fiona Aeronwen is alright. The way the stress falls on the syllables makes for a nice sound, but the -a A- is a little awkward.
I can NEVER find good combos for
Fiona as a fn! I've got nothing.