In light of just finishing Till We Have Faces (see below), I was interested to read the following in a letter from Lewis, to Katherine Farrar, Feb 1955:
. . . my version of Cupid and Psyche. Apuleius got it all wrong. The elder sister (I reduce her to one) couldn't see Psyche's palace when she visited her. She saw only rock and heather. When P. said she was giving her noble wine, the poor sister saw and tasted only spring water. Hence her dreadful problem: 'is P. mad or am I blind?' As you see, tho' I didn't start from that, it is the story of every nice, affectionate agnostic whose dearest one suddenly 'gets religion'; or even every lukewarm Christian whose dearest gets a Vocation. Never, I think, treated sympathetically by a Christian writer before. I do it all thro' the mouth of the elder sister.
--Collected Letters of C. S. Lewis: Narnia, Cambridge and Joy 1950-1963, 590
(Gav, this would seem to vindicate your comment below...)