You've got a lot of good advice and suggestions so far. I think I'd hold off on threatening the shunning aspect; that's what THEY do.
Nevertheless, I believe you need to be firm, completely clear and unequivocal about it. Being a teacher she must know that she could not talk to her students about her religious beliefs (assuming she taught in a public school).
You could also ask her if she wants you to respect HER religious beliefs even though you don't agree. Then tell her that she MUST likewise respect yours.
00DAD