I prefer it spelled
Aria, and then I like it. The creative spelling Arya removes the beautiful meaning from the original
Aria, and in my humble opinion it doesn't look as good. I love
Aria, though. :)
I suppose you could also feminize Arieh/Aryeh, which I believe is pronounced the same way (does anyone know for sure?), although again that changes the meaning from "song" to "lion," which I don't think is as pretty for a girl.
Another suggestion/possibility: You could use Arya as a nickname for something like
Arwen.