Well, Sinbad said in a previous chapter that there isn't a direct proof that Sherazade is a magi, but since she helped many dungeon capturers & built an empire over 200 years, people assumed she was one. So it's very probable that she might be a fake.
And I wonder how did she live all those years? Did she use some magic? or was there really a magi Sher 200 years ago and this one dying created clones of her (or just descendants?) to protect the image of her country? Wait, where's the king of Reim anyway?