The characters in Mari's name mean "truth". Which I just realized is the same "truth" that's in the title of her scriptures. So, you can read that as either "The Writings of Truth" or "The Writings of Mari".
Incidentally, Yuu's name means "gentle".
At the Juujouin Angelic Garden, she was Yuu's roommate. Now, she is the adoptive daughter of the principal of the Holy Grand Cross Girls' Academy.Juujouin Mari