They haven't met face-to-face yet. Did the student six ever tell her? Seems like someone might be getting ninja-trolled here.
Treelight 'Harmony' Sparkle is best princess
(My favorite non-equinoid character, followed by Discord. - As for equinoids, Silverstream is lovely, too.)
UPDATE: Now my nickname for her is Harmony Sparkles, and her rarely-used middle name is Actually.