Who is Agnes Deigh from The Recognitions a Novel and what is their importance?

This satirically-named character whose moniker derives from the Latin "agnus dei," or lamb of God in the Bible, is a sun-tanned woman with a commanding voice who is married to a Hollywood screenwriter. In a sense, she is a distillation of the wealthy liberal New Yorker who is careful to observe all the politically and culturally correct behavior but who nonetheless is the subject herself of much envious gossip. She is described as "that full-blown flower whose fey petals curled and yellowed round its white spore-bearing carpel."