My old elementary school principal saved me from drowning when I was in 1st grade.  I'm eternally thankful for her and hope she's doing well wherever she is now
thats an amazing memory to have, have you since visited her or sent her a card? 
That's a great idea but I don't know where she lives
I would call the school and see if they can disclose that or maybe they can accept the card from you to give to her! 