What is the guardian spirit of a girl called?

The guardian spirit of a girl in ancient Roman culture is referred to as "Iuno" (often spelled as "Juno" in English). Iuno is the goddess who presides over marriage and the well-being of women, particularly as a protector of young women and girls. She is often invoked for protection during their transition from childhood to adulthood.

Flora, while a significant goddess associated with flowers and the spring, does not serve the particular role of a guardian spirit for girls. Nona is one of the Parcae, goddesses of fate, but her role pertains more to childbirth and life rather than being a guardian spirit. Jupiter, the king of the gods, is primarily associated with authority, thunder, and the sky, but he does not have a specific connection to guarding or protecting girls.

Thus, Iuno is correctly identified as the appropriate guardian spirit linked to girls in this context.