Um, you might think it outmoded. But the majority of the modern world still does it...
I think she's doing what she wants. Which is all that matters cause its her life and opinion right?
So.. then it comes down to a big thanks for your warning and offer of advice, as that is the correct thing to do. But to follow it up with more blather after she has thanked you for your offer of advice, is then you trying to IMPOSE your beliefs on her.