Aoife is a name I've never encountered. Intuitively, I'd say AY-fa, however, this site says EE-fa. Now I have known a few Dierdres who pronounced it DEER-dra but they were all called
Dee. Can't say I'd use either, but they're fine for someone else's child. On second thought,
Aoife is rather pretty; I might consider it.
I live in the Southeast US.