You may be sick to death of hearing about her, so let it suffice to say that I have at least two more that I expect to read and report on (although, depending upon my endurance, I may pursue the rest of the available opus.) Those two shall be a "pair" even if not invested with the same characters (about this latter I do not know)--they are: The Girls of Slender Means and A Far Cry from Kensington I regret I have not looked into Ms. Spark's writing extensively before now.
What is intriguing about Ms. Spark is, like many great writers of the recent past, she takes questions of faith quite seriously. They may not be spelled out word for word on the written page, but every book deals with the themes of morality and religion to a greater or lesser extent. In some, i.e. Memento Mori, The Prime of Miss Jean Brodie and (so far at least) The Girls of Slender Means it is to some extent the driving force of the narrative. In others, Aiding and Abetting, Not to Disturb, and The Finishing School religion isn't overtly the theme, but it certainly is a powerful element in the overall structure.
We'll see how it plays out in the next couple of books. Regardless of how morality and religion saturated they might be, the crystal-clear clarity and concise, powerful prose of her novels makes her a compelling and serious novelists, even though most of her novels are not dead-pan serious.
Spark has long been one of my favorite writers. I will always be interested to hear anything you want to say about her.