I read your conversation with the mother of the 15 year old daughter, and I can say as an 18 year old former christian that the quickest way to get your daughter to “turn away from the lord” is to try to repress her free thought and questions about religion.
The thing about questioning is that it can never be wrong: either it turns out that she learns the truth (good) or she gets strengthened in her current beliefs (also good). Either way, attempting to put up a shield is only going to backfire when she begins resenting you not treating her as an individual who can think for self.
I agree with you that questioning seems like the right way to go no matter what side of the discussion you are on. Unfortunately, there are many religious people who would disagree.
Some of them would say that true faith means not questioning, but to me that sounds like a recipe greatly increasing your risk of being drawn into a cult.