From Hunter Family Register: "Polly died when she was two years old, under such peculiar circumstances that it was thought that she was poisoned by the colored nurse." Her father died a few months later, just before the birth of Polly's sister, Jane Alexander Thompson.
http://trees.ancestry.com/tree/5767874/person/-1352270580/media/1?pgnum=1&pg=0&pgpl=pid%7cpgNum