Why is Scout the person who is chosen to explain things to Miss Caroline?

Scout has a strong personality and sense of self. She is often unfiltered. She also believes that Miss. Caroline simply doesn't understand and is trying to be helpful. She also felt she had "special knowledge" other didn't because of her father's interactions with the family. 

I tried again: “Walter’s one of the Cunninghams, Miss Caroline.”

“I beg your pardon, Jean Louise?”

“That’s okay, ma’am, you’ll get to know all the county folks after a while. The Cunninghams never took anything they can’t pay back—no church baskets and no scrip stamps. They never took anything off of anybody, they get along on what they have. They don’t have much, but they get along on it.”

My special knowledge of the Cunningham tribe—one branch, that is—was gained from events of last winter. Walter’s father was one of Atticus’s clients. After a dreary conversation in our livingroom one night about his entailment, before Mr. Cunningham left he said, “Mr. Finch, I don’t know when I’ll ever be able to pay you.”

That she believes scout and he want to be helpful and tell miss Caroline