What is the story of Grandma Ghost?

Tully's great grandfather married a woman named Sarah Sawyer. Jubal Mars took his new bride to New York City in 1859 and as a special surprise, takes her to see the first exhibition of Heart of the Andes. Sarah is so taken with the tropics the painting depicts that she is gone the next morning, leaving her husband only a note telling him the tropics is calling her. In Mars family folklore, she became known as Grandma Ghost.