Born in 1890, Ms. Gurlitt was the elder sister of Hildebrand Gurlitt, a dealer who bought art for Adolf Hitler’s planned “Führermuseum” and acquired the cache of more than 1,200 works found in his son’s apartment. Ms. Gurlitt’s work is virtually unknown — partly because much of it is thought to have been hidden for decades in her nephew’s home, alongside the Matisses, Monets and Munchs. Those works remain out of public reach for now. Yet some of Ms. Gurlitt’s melancholy, Expressionist images, many of them lithographs, did find their way into the possession of friends and family members.