Are you really asking what we would actually do, or what we think one SHOULD do? There's a difference there, because many of us (or me, anyway,) don't always behave as we know we ought.

For what it's worth, I also have a teenage daughter, so this question isn't just academic. It could happen to her too!

So, what I suspect that I SHOULD do: Let her do her thing. That doesn't mean that I would stop doing MY thing, of course, and I would have some sharp words for her if she tried to convert me! But overall, her faith is her business.

What I suspect I would ACTUALLY do: I'm just not that good at keeping my damn mouth shut. And I get SUCH a kick out of being a pain in the ass. I would probably go overboard with displays of piety. I would start cooking Kosher for her, just in case. I would question every outfit she wore, asking her if she thought that Jesus would approve. Likewise for every book she read, every TV show she watched. If she dared to bring a boy home, I would ask about his understanding of a Christian marriage.

Christmas and birthday gifts would be Jesus-themed, of course. I would ask her to lead us in prayer before every meal. And snack. And glass of water. Hell, maybe I'd even join her church for a while. Kids just love it when a parent goes overboard like that, right? (Yeah, that was sarcastic).

And THIS is why I am a terrible mother. But, she puts up with me anyway, so I guess it works.

If that's the worst thing she ever does , consider yourself fortunate. Could be a lot worse ...

Like Amy said few comments below , I am a cuntasaurus as well . I will be sooo accepting and soo understanding and so ok w her new founding love for any religion .
Sure . I ll make sure I ll refresh my studies about that religion faster than u can blink an eye , then I ll make sure I ll create oppurtunities for her to choose btwen her holy book’s preaching and life . Then I ll sit back confused and sad , “ but I thought u were a Christian now “?
There are so many things to knock god out of his throne in daily life , that it won’t take me more than two weeks vacation w my child anywhere for her / him to say “ fuck that shit “.

Humanity and the suffering of humans bcz of religion is everywhere . I mean everywhere . As long as I have a finger I am not afraid to point it out . U can’t make everyone to see it , but nobody can stop me from pointing , and I won’t go down without fighting , ever . Not me , not on my time, not on my dime . If my child , and only for my child , ( lovers and family member get no free pass in my book ), still choses to remain blind , I will be sad , but I ll fake an acceptance at the end , bcz i will rather be at my child’s life and able to help when needed w serious issues , instead of been cut off and not knowing when my kid needs me at all .

Ultimately, if she's 18, that's her choice.

Atheists might think it's weird, we might think it's unfortunate, we might think it's a backward step - but at 18 she's old enough to make that decision.

See the Book of Leviticus for instructions. I think it says something about selling her into slavery.

My daughter flirted with a Christian church for awhile because her friends went there. You need to be patient; don't jump on it; remember she's had the right training and she's just experimenting right now. She figured it out.

I would try and find out why first , you can't choose family . Arguing only causes pain and adults are responsible for themselves

Nothing, happened to me. If my adult child wants to be a believer , I have no right to stop that. Im still an Atheist, believing in nothing. At first , he and his wife try to save me, but realy friendly and unavasive. That stoped after I had to leave the church service , they invited me to. I could not stand it.
Every once and a while the topic of God and the act of believing , comes up again. But no arguments.
Its enough to be yourself, religious believe is a state of mind, and everybody is in controll of their own mind.

Well, the child must be free to make that choice, whatever you like it or not.

Rewrite your will.

Depends on what they do with it. Just becoming a Christian isn't necessarily a bad thing. Becoming a Christian and then running around telling everyone else that they are condemned to burn in hell and that the world must change to conform to their new belief system, well, that would start a very long conversation which may end in disappointment for both of us.

I have one atheist child and one Christian child. I want them to be their own people and religious beliefs are part of that.

Humans are animals who evolved instincts to gather in groups for safety. Our animal instincts are still active, and we generally do seek out groups to belong to, and beign acepted by a group gives us a sense of safety and well being.

Religion is an artificial construct to fulfill instinctual drives to belong, because belonging makes us feel safe.

I think it is best for atheist/agnostic parents to educate their children so they might over come their instinctual drives to belong, and if they understand just what it is that might make them attracted to religion, they wouldn't be as subject to peer pressure influence to join a religion.

Not being a parent, it’s easy to say you have to let young people find their own way. Hopefully you’ve given her the right tools to look after herself.

Nothing

Fortunately most religious folk and especially Christians do not practice what they preach and church going is relative harmless.

Don’t worry too much and let young adults make their own mistakes... you will know when to voice your opinion or warning.
She will ignore you anyway.

I personally never heard of anyone going from Atheist to Christian. Only the exact opposite.

I'll take it from the flip side. Going from Christian to Agnostic. What compelled me is the overwhelming lack of evidence for Christianity. The only link historically for Jesus is a Jewish Historian named Josephus. Josephus was born 5 years after Jesus death. That would be similar to a child born in 2025 and telling the whole world what it was like to live during Donald Trumps presidency.

Plus if Christianity is the truth then why do the preachers have to resort to fear tactics like hell in order to scare the crap out of people to get saved.

The history of the Catholic church should also be something good to tell her to explore. The catholic church was an expert in torture and death to people who didn't believe. Back in the early years there was an actual hell if you didn't believe. It wasn't the Lake of Fire it was the Catholic church torture.

You have to let her explore life. This may be a faze in her life. Give her a book on paganism to read. Tell her there are lots of options out there.

I have a daughter, just turned 19. She was raised atheist and claims it proudly. If she started attending a church, I would simply ask what it was about the experience that she liked. If it was just being with friends, it’s fine. I would ask how she felt about what was said in church and whether she believed any of it or not.
I don’t see my daughter doing this any time soon. She is far too strong-willed and resistant to peer pressure of any kind. But I would keep the dialogue between us open and supportive. I think she would find it boring and full of b.s.actually.

Presbyterian is Theist Lite, at least.

She could have been hanging out with the kids who went to a church where people fall to the ground and twitch and no one calls an ambulance.

What can any parent do but give a child as good a foundation in reason as possible and then let them out on their own to learn and explore. Be there for them if they seek your opinion or advice and pick them up and dust them off when they stumble and fall.

Even if she was younger than 18 what you gonna go? Give her a time out? She is probably just doing it for some sort of acceptance. I don't know her so I don't know. But most people raised in non religious homes don't become religious. Maybe she is rebelling at her parents. Kids do that. Why don't you just talk to her rather than talk to a bunch of strangers?

Was your daughter ever aware, even obliquely, of any pagan observances, teachings, books, symbols, practices or rituals while growing up? Is it possible that, much like Emperor Constantine, she's turned her back on one religion in favor of another for political purposes?

Why worry, if that makes her happy. She probably has heard a lot from you about no god so don't worry, she will do what she feels is best for her.