The sister who can conjugate Latin verbs.
She also understands Shakespeare.
She has most of the opera Les Miserables memorized.
She can name all of the 44 U.S. Presidents.
She can tell you the leaders of World War II from both sides, Axis and Allies.
She can recognize classic paintings and tell you about the artist at a glance.
She knows the capitols of all 50 U.S. States.
Oh and did I forget to mention:
SHE JUST TURNED SIX YEARS OLD.