definition of ava and cassie in the book "a gathering of days"

Cassie Shipman is fifteen-years-old, and Catherine's best friend. The girls are together all the time, and their friendship is only tested when Cassie voices her need to do the right thing, and Catherine disagrees with her. Their disagreement, however, is only temporary. In the novel's conclusion, Cassie dies of a fever.

There is no character by the name of Ava in the novel.