Who is Mrs. Berryhill from Mick Harte Was Here and what is their importance?

Mrs. Berryhill is the principal at Mick and Phoebe's school. The day of Mick's death, Phoebe is taken into Mrs. Berryhill's office. She remembers thinking that Mrs. Berryhill needed a Tic Tac for her bad breath. Later, when Phoebe goes back to school on the first time, she talks back to Mrs. Berryhill because Mrs. Berryhill continually refers to Mick's death as a loss. The next time she is called into Mrs. Berryhill's office, Phoebe believes she will be given detention, but instead Mrs. Berryhill has a representative from the PTA in her office who wants to ask Phoebe about participating in a bicycle safety assembly.