How does the author reinforce the theme " Things are not always as they appear" in chapter 11?

The planet of Ixchel represents the need for individuals to see the inner beauty of things, not just the outer beauty of the world. The planet, being devoid of most light, of course, does not provide a facile sense of beauty or wonder. But it is the beasts' inner goodness that suffuses the planet with light.

The beasts refer to a biblical passage, again from the Book of Romans, that illuminates their mode of living: “We are called according to His purpose....” The beasts do not attempt to understand the world according to its outer beauty and dimensions, but instead rely on the inner goodness of the universe - what some might call God. This completes L’Engle’s cosmology for the book, one based on both outer beauty and inner goodness.

The fact that one of the characters ultimately gets the name "Aunt Beast" shows that the creature is obviously not attractive and yet is able to do wonderful things for Meg. who is worn out and not feeling well. Ultimately, Aunt Beast is not a beast at all and helps Meg so much that she wakes feeling incredibly rested and well again. Obviously the beast is not what it seems.