Almost every one of her works features a main character who is Catholic and that is woven into the everyday life of the character–there is usually a reference to attending Mass and many times a priest is a secondary or walk-on character (and I’ve yet to see a negative portrayal of one in any of her books.)
Mary Higgins Clark writes “romantic suspense”. Nothing in the books comes out and whacks you over the head with Catholicism, but the “flavor” is there, it’s natural and never forced. Her memoirs, “Kitchen Privileges” is also a great read. She is a life-long devout Catholic.
I guess it would be more appropriate to say that her work is fiction that happens to feature Catholics who are NOT disenchanted, psychological basket cases, or embroiled in some conspiracy with the Vatican!