I was in church camp and eventually came out queer and supported by my family even though they're the ones who put me there. I'm pretty sure it was just a decision for cheap daycare. I also remember nothing from Church other than a fear of God caused by the fact that I was a kid and something about an all-knowing being creeped me out.

Basically: Expect questions. Know that your sister will be confused why the teachers and you may have differing opinions. Explain brains are different for everyone, so opinions are different for everyone. Try to emphasize that she is allowed to form her own opinions too and no one, not even you, can take that away from her. But let her ask questions. Let her ask many questions, because if she's asking questions, that means she's questioning things that are being taught to her. And as her big sibling, you may be a stronger source of inspiration than the teachers are at this age.