Looking over the Van Natten material, I have to say I quickly came to the impression that she or they are a bit off the deep end.
I would have to allow that part of my response stems from having little patience with those who are convinced that everything Roman Catholic is from Satan. Those who claim this, I believe, are profoundly misguided and lacking in good judgment and clear thinking.
Here is one example of their lack of clear thinking.
At one point the site discusses Lewis' supposed 'sun-worship'. Much of this seemed to be based on very speculative interpretations of the symbolism Lewis uses in his Narnia books, e.g. the Lion the WItch and the Wardrobe. For example:
Van Nattan wrote:Let's begin by looking at the The Lion, the Witch and the Wardrobe.
p.65 "At the name of Aslan, Lucy got the feeling you get when you wake in the morning and realize it's the beginning of spring."
p.74 "Tell us about Aslan...once again that strange feeling - like the first sings of spring had come over them."
p.74 "An old rhyme in these parts...when he bares his teeth winter meets its death and when he shakes his mane we shall have spring again."
The plot here, as those who have read the Chronicles will know, is that the "White Witch" has bound the land of Narnia in a perpetual winter which can only be broken by the coming of Aslan. This makes perfect sense in the context of the solar deity myths. The common story line is that a goddess kills the sun-god on mid-summer's night and thus winter comes. When the sun stays up longer on the mid-winter solstice (commonly celebrated under the disguise of "Christmas" today) he has triumphed and conquered death, thus bringing spring. We find this ritual being observed by the Jews in Ezekiel's day. Ezekiel 8:13 He said also unto me, Turn thee yet again, and thou shalt see greater abominations that they do. 14 Then he brought me to the door of the gate of the LORD'S house which was toward the north; and, behold, there sat women weeping for Tammuz. This was the summer death of the sun god, Tammuz, that they were weeping for. The remainder of this story will be discussed further along. (Notice the circle of flowers in the illustration above. The imagery is not wasted. The circle is a common symbol of the sun, and a basic symbol of ritual magic. Wreaths are used in witchcraft both to cast spells against people and to bring "good luck.")
This [cordial] presented to Lucy is said to be made from fire-flowers that grow on the mountains of the sun. According to the book by Jobes, fire flowers themselves represent the sun. Here they are said to grow on the mountains of the sun which are associated with Leo, the lion of the zodiac. In fact, the name Lucy itself means "light." It is from the Latin, and relates to "luce," as in Lucifer. Lucy might well be considered an "illuminated one."
p.156 The mice came to chew away the ropes that tied Aslan to the stone table upon which he had been ritually sacrificed by the witch. Lewis strongly emphasizes the sun rising in the "East" (note: capitalization) as the mice chew through the ropes to free him for his resurrection. "...the sky on the East side of the hill was a little less dark than it had been." After they gnawed the ropes through, "The sky in the East was whitish by now."
First of all, the fact that this event occurs at dawn and that Lewis makes so much of the sun rising is significant in that the sunrise is viewed as the sun's resurrection in the myth mentioned above. That is, Lewis is telling the tale of the sun's daily death and resurrection in careful, but hidden (to the uninitiated) detail. To the followers of sun worship, this is all very easy to see.
It looks as if the Van Nattan's came to their conclusion by some leap of imagination, and then find this imagination reinforced by their conspiratorial and imaginative reading of Lewis' works. The seem to ignore the fact that even the Bible uses light and the Sun as a metaphor for God.
As a final comment, certainly the idea that Lewis might believe in theistic evolution would be a red flag for the Van Nattan's. They seem all too eager to discredit him because they seem too attached to the particulars of their own beliefs as the only 'true CHristian' beliefs.