Who is Mrs. Somebody-or-other from the PTA from Mick Harte Was Here and what is their importance?

Mrs. Somebody-or-other from the PTA is the lady who approaches Phoebe about participating in the bicycle safety assembly. She indicates to Phoebe that she believes that if Phoebe spoke at the assembly, it would have a big affect on those gathered. Although Phoebe first brushes off the idea, she later changes her mind and agrees to participate.