1) The Empress's Aspect wasn't set until Return to the Scarlet Empress.
I know for a fact that it wasn't "Earth, secretly, until RttSE revealed the truth to the world!" because I've spoken to the person who wrote it. Notably, Grabowski always replied with "Does she even have one anymore?" when asked the Empress's aspect, so for the Earth thing, as with everything in RotSE, take it with a grain of salt.
2) There's a bit in Aspect Book: Air that suggests some bored secret society in the Shogunate aristocracy was engaged in a large-scale game of what's essentially sociopolitical Nomic
(see "From a report by Magistrate-Captain Riarda Rikvashta," beginning page 63), and an offshoot of that involved a Dragon-Blooded breeding project. The hints are the Empress is one of the outputs of that. So there's a reason for her unusually strong bloodline.