Also as for comments about Easter. Most people don't celebrate Easter for the religious version. Easter is pretty much the modern version of Ostra (The goddess of spring and dawn), the spring equinox.
The Easter bunny is from the hare and rabbits from Ostra.
The Easter eggs represent fertility (Since a lot of newborn animals and fresh flowers are seen in spring)
The colours of Ostra are Pale pink, pale green, yellow and silver. Which are usually seen on Easter eggs.
Easter eggs were decorated by children and hidden for finding even in old europe for thanks for spring. The spring goddess sent the painted eggs back to children using the rabbits with baskets.
Also rabbits are closely linked to easter/Spring and is also connected to the moon. So easter/spring being the birthday of Princess Luna who is the moon of the Empire makes sense.
Also about the spring equinox being the birthday for Princess Luna, Equinox means 'equal night' so the aesthetic of night is once again being used.
And this world is technically created from a book from someone from our world so it makes sense that this world has seasonal holidays. It probably also has Yule (Aka christmas/ Winter solstice/ Midwinter)