What is one thing that Mattie vows never to do in the book Fever 1793?

Fever 1793 is set during Philadelphia's notorious yellow fever epidemic in 1793. This highly contagious disease thrives in hot weather, and the summer of 1793 in Philadelphia is hellishly hot. Deeply religious folk liken the city to Hell in the midst of all the intense heat and suffering. Growing up is hard enough to do for a young adult like Mattie; it's harder still when you have to do it slap-bang in the middle of a deadly epidemic spreading like wildfire and with diseased corpses piling up in the street. It's fair to say that Mattie, like everyone else in town, is sick and tired of broiling away in this terrible inferno. So it comes as no surprise when, after yet another week of ceaseless heat, she vows to her grandfather that she will never complain about a cold day ever again.