Not surprisingly, the public flocked to see the well-conceived Mary Cassatt exhibition at the Art Institute of Chicago, standing in line to buy calendars, posters, refrigerator magnets, and coffee cups adorned with her beloved images. Yet the exhibition curator, Judith Barter, intentionally downplayed the sentimental side of Cassatt, opting instead to show her evolution as a “modern” artist. Ninety key works, including paintings, pastels, drawings, and prints, highlighted Cassatt’s progress from a young artist studying...