what was the uncertanty discussed in chapter 2 and 3

They find out that Polly is dead.Polly is a long-time girlfriend of Mattie Cook - the two girls grew up together. Mattie's mother explains that Polly died of an undiagnosed fever, and she ensures that Mattie is not ill. Mattie wants to visit Polly's house and attend her funeral, but Mrs. Cook forbids it. Mattie believes her mother's fear of fever-contagion is ridiculous but abides by her mother's wishes. Their is uncertainty about this sickness.