I still think you could do Luka, but here are some other options.
Sakura Hanasaki from Wedding Peach
Utena Tenjou from Legendary Girl Utena
Miyuki Takara from Lucky Star
The Eastern Princess from Princess Princes (this is kinda-sorta crossplay, if you're ok with that)
Princess Grace from Twin Princesses of the Mysterious Past
Haruna from Watashi no Messiah-sama
Hinagiku Katsura from Hayate the Combat Butler
Ai Fuyuumi from Ore no Kanojo to Osananajimi ga Shuraba Sugiru
Kyrie Florian from Magical Girl Lyrical Nanoha A's Portable: The Gears of Destiny
Ran Tendo from The World of Narue
Kiriri Kaibashira from the World of Narue
Mami Tomoe (Puella Magi Madoka Magica) - 40% complete
Queen Elsa (Frozen) - 15%
Elphaba [Defying Gravity inspired dress] (Wicked) - 35%
Gryffindor and proud!!!