Yeah, but I want to stick to Sun and Moon in LatinGlish because that way people quickly get the picture.
Orion sounds too much in outer space and
Luna may cause the girl to be bullied as "Loonie" or "Lunatic" when she's in high school. I figure Lunaria is better since it's also the name of a flower that was named for the moon.
Solarion, on the other hand, is a corruption of "Solarian", which means "of the Solar System" and would be an effective ID tag if this kid became an astronaut and settled on an extrasolar planet in his early lifetime.
(It's a remote possibility in my lifetime, and it will be a good probability in his...)