Sorry if it came out sounding wrong, but I think you misunderstood me. It's my fault, I've been reading too much De Sade lately.
I never meant you ought to lie, but rather that you show her the truth. That there are certain things in this world that prove God wants us to be happy, and voluptuosness is one of them.
As for damaging another person, I don't see how a sharp dose of reality could cause more temporary harm than lasting good. Something will awaken her to it eventually, and if that thing is you, you can make it as gentle as possible.
That Catholic girl I was with is still devout. She just enjoys life more.
And if this is inarticulate and contradictory, pardon me.