If I ever got Princess a sister I always wanted Duchess as a name to keep with the 'royalty' but now have come across something I love more. And yes, it makes me a nerd! It's
Khaleesi, means queen in 'Dothraki', a made up language on HBO's 'Game of Thrones'.
I love it! See, I told ya, very nerdy.
I also love Luna. I wish I'd picked more of an uncommon name for Princess, though she's my Princess, everyone seems to have a Princess! That may be something you want to keep in mind.