I think it is really perfect. Sweet, organic, simple, and elegant. Not out there at all.
I think Calla is beautiful! It may present some difficulties. It is essentially "call-a". Whatever her surname is or may become could present difficulties with her name being Calla.
Variations of Lily:
Lilium (the genus name of many lilies. Not really a name used, but I kind of love it.)
Names meaning Lily:
Kielo (Finnish: lily of the valley)
Names that could derive Calla:
If you love Calla you should use it. It's a wonderful name.
Glad you've gotten positive comments about Calla as it's my DD's name and we love it. It suits her and everyone seems to like it. We do call her Calli at times. Only problem we've had in Finland is our pronunciation is different that the Finnish form Kalla. I've met one little Finnish Kalla and I have to be careful that I don't say 'kala' which is fish in Finnish. All 3 are pronounced differently and I sometimes don't get the Finnish form right.