Our Daily Bleg: What's the Word for …

From a reader named Raymond DeCampo comes this interesting, poignant bleg. (Read up on blegs here; send your own blegs here; and see some other new Freakonomics-coined words here.)

My wife and I recently undertook the task of securing our son’s future in the event we would not be there to secure it for him.
In the process I realized that while our choices for guardians were good people and good parents themselves, they did not share the same value of education which we share. We soon realized that while we had appointed godparents to watch over his moral development, we would feel better if an analogous figure was watching over his academic development. Thus my wife’s sister became his academic “godmother.” The bleg is: what should we call her?