I think I would prefer Edwynna (ed-WYNN-uh) to
Edwina. I know it is less established (i.e. not established), but I think the sound is softer and more settled. It reminds me of
Morwenna. Then you could also give it a Tolkien feel and experiment with Eowynna if you really want to get whimsical. Don't mind me. I've had too much coffee.