Safeguarding my daughter against Christian teaching at school? Have written a letter.?

It appears you have answered your own question in the final paragraph of this post. It also seems that you are raising your daughter to be an intelligent, independent thinker. Because she has parents who are atheists, she'll never believe in crap such as: God, the Resurrection, the Immaculate Conception, Heaven, Hell, etc. You're doing the right thing; stop worrying.