I like both a lot.
Milagros ("mee-LAH-gros") is also a personal favorite -- it means "miracles" in Spanish. I have a friend named
Milagros and she is drop-dead gorgeous, very pale, milky skin, gold-brown hair, huge almond-shaped eyes, very slim and slender... I always associate the name with her. Sorry, got a little off-topic there. Of
Mira and
Nessa, I like
Mira best.
Mireille is another name that resembles "miracle," I think.
Mirella is the Italian form of
Mireille and another option.
Mira could be a nickname for
Mirella, or
Miranda or
Mirabelle. Or simply name her
Miracle, which is a name in itself.