Elowen - will get 2 different pronunciations
Lowenna - nice
Eirwen - grannyish not in a good way, the Eir will probably get mangled
Similar names:
Alwen/Alwenna, Rowella, Rowena, Morwen/Morwenna
Eirlys, Eleri, Eira, Eluned, Aeronwy, Myfanwy
Not ANWYN! That really is not a name. Anwen is.