Frida Kahlo and Diego Rivera met in 1922. He was a famous muralist. She was 15 and impressionable. Kahlo began to watch Rivera as he painted. He would tell her stories of Paris, the war, and the world of Picasso, Modigliani, and Breton. Though the pair went on to marry, Kahlo did not remain in Rivera’s shadow. He encouraged her to paint—“You have a gift,” he said—and he was right. Zooming in on these two leading figures of Mexican modernism, this show places their work alongside fellow Mexican modernists. —E.C.