Despite her popular success, Sister Wendy knows nothing about art.
In attempting to bring art appreciation to the public, there is nothing more noble than what Sister Wendy is doing. What I question is the kind of appreciation she brings.
Sister Wendy's methodology is to tell stories about paintings. That is, she tells stories about the content of paintings. But, there is more to art than content. If content was the only important issue in art, there would be no need for various artistic mediums. After all, photography is just as good, if not quite a bit better, at factual representation than painting. Or, for example, if the idea content of fiction was the only reason for reading literature, there would be no reason to read literature. Non-fiction essays or histories would do just as well. Indeed, it requires little or no training to move from the unique, intrinsic character of a work itself to the ideas or facts with which the work is concerned. But, no one, aside from perhaps Sister Wendy and her ilk, looks at art, listens to music, or reads literature simply for content, for content alone can do nothing to reveal the sources of pleasure that a particular work affords.
Instead, aesthetes "prattle on about color, technique, or social context" because those ingredients add to, not distract from, the experience of art. For example, critics study color theory because color effects people's emotions. Understanding how an artist manipulates color to achieve a certain effect helps one understand how art achieves its emotional impact.
Indeed, study of artistic technique is vital for appreciation of the arts because without it there is no vocabulary with which to discuss one's experience of enjoyment (and without vocabulary, perhaps there is no thought or enjoyment). And, even if content held preeminent position in the aesthetic hierarchy, techniques such as color, form and composition, positive and negative space, or meter, structure, rhyme scheme help explicate the content.
After all, what is aesthetic experience if not the alert perception of art?