I have a cute, little headcanon which states that Rosalina is actually an all powerful luma taking the form of a human.

[MajorTom1972]

Since lumas can shapeshift into pretty much anything, I don't think it's unlikely to assume that Rosalina is one too, but more specifically a queen luma who asexually reproduces new lumas, kinda like how a queen bee gives birth to all of the bee children in a hive.

P.S. Keep in mind that I said "headcanon" and not "theory", which is different from the theory.