A personal sit down the principle where you discuss if the teacher should be talked to by you or just the principle or all three of you..
This is something that will get worse.
I was taught to never bash any other religion but I will certain people and this woman obviously doesn't respect that not everyone believes in God.
Children are very important, and they learn from us. If someone they see on a day to day basis is telling them something you don't want them to learn you have to step up.
But be diplomatic about it respectful that this is what this woman beleives which is why I think a sit down with all three of you will be a good thing. Becuase she'll be more inclined to listen to the issue with you in the room and not just the principle telling her. Plus you get to know exactally what she says and what she is told so you don't feel left out.
Just telling your daughter it's not true doens't help. Specially if the teacher keeps countering that.