Why does Mary Grace call Mrs. T. “A warthog from hell”?

Actually, I would have hurled a book at Mrs. Turpin too. She is pretty damn annoying. Mrs. Turpin is in the doctor’s office yammering with Mary's mother about how good it is to be rich and white. Mary is described as teenage girl who is quite overweight. The girl is reading a book on human development. Mary is obviously listening to the conversation because her body language gets very tense as Mrs. Turpin thanks Jesus for being white and owning land with pigs. Finally when Mrs. Turpin is in the middle of a discussion about sending all Negros back to Africa, Mary hurls a book and attacks her. Mary has obviously had enough. The fact that she is a fat teenager has nothing to do with her intelligence or sense of social justice. Mary stands up for what is right in a moment of emotion and disgust. Then she tells her off the best way she knows how. Way to go Mary!