How is Miss Caroline hurtful in Chapter 3?

In Chapter Three, there's a big scene when Miss Caroline screams upon seeing a louse ("cootie") crawl off of the head of one of the boys in the class. This boy, Burris Ewell, comes from a family so poor that Atticus says they "live like animals." Their children come to school on the first day of the year and then are never seen again. The children inform their teacher of this, explaining that "He's one of the Ewells." Miss Caroline wants Burris to go home and take a bath, but before he leaves the room for the rest of the year, he yells crude insults at her and makes her cry.