Wow, Canaria, wooooooooooooow, did you seriously not remember anything about Gracie's character from the book? I'm sure her status as a woman instead of man came up AT SOME POINT.
Back in the first chapter, Gracie was referenced to as Duchess Lancaster, so unless there is some mistake in translation it seems that she can and will inherit her family's title. Hopefully this is addressed in the next chapter.