Certainly you know that you did not traumatize her by doing that, we Catholics are raised to know better, and presumably, your son was likely raised to know better than to even ask such a thing - and he knows this regardless that he lost the faith. Traumatize her indeed - baloney!
It's a tragic situation, one that all of us trads, or at least every trad I know has dealt with in some way, and it's only worse because she is 18 years old so the world expects you to simply accept which ever way your "adult" daughter chooses to go. The devil wants that soul so bad and he doesn't care whether he uses smiles or gnashing teeth against you to get it.
We are ready to just say you know what...you raise her. SHe is our youngest ..of 11 chlidren. We are in our 60's. Any suggestions.
That sure seems like the best way out, but is it? Maybe for you, but only you can guess if it will even matter at all to your daughter. Will letting her go help her come back to the faith, or can it only help her in her quest to completely lose it?
I can only suggest that you keep trying to do what is right as you have been - certainly God knows you've held up your end of the bargain to raise her in the faith and all the tribulations involved in doing that, but if it comes to a point where you can no longer control your child, then at 18 years old, you can no longer control your child. Sometimes holding out hope that she will come back to her senses does more harm than good - other times, when they regain their senses, it ends up being worth the battle.
If I could suggest anything, I suggest that you remain steadfast and remain uncompromising and do what you need to do to save your own souls, this is what God expects of you. There actually are times when you need to simply let go for the good of your own soul and that of your other children. I don't say that this is that time, that's your call and as tragic a thing as it is, sometimes that's the best thing that you can do - and you do it for the good of your own soul and the souls under your care.
It's a terrible situation, I will pray to Our Lady of the Smile for your family. Get a statue of this Lady and put it in your house, the sooner the better. I cannot say enough good about her, I will only say she has done wonders for us and other trads that I know, all *were* in similar situations as yours. The key word there is "were".