Why does Meg get in trouble at school? How does the principal make matters worse?

In the first chapter of A Wrinkle in Time, we learn that our main character, Meg Murry, is not doing well in school in spite of how smart she is. In the second chapter, which is titled "Mrs. Who," we see Meg in school, tired from the lack of sleep she got the night before. When Meg cannot remember the answer when asked about the imports and exports of Nicaragua, her teacher, Miss Porter, and fellow classmates laugh at her. Meg becomes angry, and the following exchange happens:

"Who cares about the imports and exports of Nicaragua, anyhow?" she muttered.
"If you're going to be rude, Margaret, you may leave the room," the teacher said.
"Okay, I will." Meg flounced out.

Miss Porter tells the principal, Mr. Jenkins, about the incident, and he calls Meg into his office during her study hall. It becomes clear that Mr. Jenkins isn't the most sensitive person when he decides that now is a good time to pry into Meg's home life and have a harsh conversation about her missing father. Meg was already upset earlier, and he makes things much worse by telling her that she should "face facts" about her father. Unlike Meg and her family, Mr. Jenkins believes that Dr. Murry is never going to come back home. For some reason, he thinks that forcing this idea on Meg while simultaneously calling her "antagonistic" and "the most belligerent, uncooperative child in school" will get her to behave the way he wants her to.