As an EYB evangelist, I share the desire to come up with the goods for your mother-in-law.
Something that struck me in looking at your Bookshelf is that a high proportion of the unindexed titles are specialized in ways that enable them to be ruled out as candidates for a seared tenderloin with tomato and anchovy sauce recipe (vegetarian, salads, drinks, burgers, cheese, seafood, Asian, etc.)
Of the 56 unindexed books, only 8 to a dozen seem real possibilities. In descending order of likelihood, they are:
United States of America: World Cuisine - Jean-Georges Vongerichten
Mansion on Turtle Creek - Dean Fearing
This Is Delicious! What Is it?
Best of De Gustibus - Marion Burros
Four Season Cookbook
The Mangia Cookbook
World Cusine Morocco
Food & Wine Mag. Quick from Scratch One-Dish
Less likely, but possible:
Fresh & Light
Jim Fobel Diet Feasts
Creative Cooking without Wheat, Milk, & Eggs
So EYB's "armchair analysis" lets you *greatly* reduce the search!
[My money's on one of the first three, but maybe that's just because they're what I'd be most drawn to if I were poking around your shelf.]
Let us know if it does turn out to be one of the books above!